| Author | Message | ||
     Peter Dixon Prolific User Username: petenlinid Post Number: 110 Registered: 8-2003 |
My vehicle SRH 40250 for the first time in 15 years failed to start at the first turn of the ignition key. There is little or no electrical power to the necessary parts for it to do so. The battery is new and fully charged. All I have that demonstrates there is some power is:interior, bonnet, boot, glove box and door safety lights. The auto door locks, cigar lighter and clock are also working. The auto transmission clicks when the lever is moved. There are no external lights nor any in the instrument panel area apart from the seat belt warning. There is no activity at all when the ignition key is turned. The windows do not work. There is an intermittent very quiet buzz coming from the speedometer area which varies slightly in intensity when the hazard light click on and off. I have to the best of my ability checked all the fuses in the fuse box and they all appear to be OK. I have tried another battery with the same result. The original new battery was installed by someone else in my home garage in my absence. The car was fine before then. I was wondering if there is some kind of electrical switch or master fuse that I don't know about that might reset the system if it has been subjected to a short of some kind. Something like the impact safety switch in an XJ6 Jag. My wife advises that the young battery installer was not the sharpest pencil in the pack. Anyway before I do anything else I would appreciate receiving any comments or advice about I might try from the members of the forum. Cheers Peter | ||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 1870 Registered: 6-2006 |
Swap fuses around or check with a test light. Don't rely on just a visual inspection. Why was a new battery being fitted? Sounds like the car may have been jump started or had a battery fitted back to front. Positive to the front on standard cars. . | ||
| Alan Dibley Frequent User Username: alsdibley Post Number: 89 Registered: 10-2009 |
Paul's tip is very relevant. Most batteries of this size have the terminals the wrong way round. RR/Bs are unusual in this respect, Alan D. | ||
| Alan Dibley Frequent User Username: alsdibley Post Number: 90 Registered: 10-2009 |
...or a poorly connected battery will pass enough power to work low-energy bits that you describe, but not the huge current needed by starters. Switching on the ignition suddenly puts a large drain on the electrics and would drop the available voltage to a level insufficient to work auxiliaries. Just thinking aloud(?). Alan D. | ||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 1872 Registered: 6-2006 |
If you connect or even flash the battery the wrong way will it will usually burn out the Shunt for the ammeter gauge - killing everything that gets power past there. The alternator diodes (being reversed) will allow a direct short and can also burn out. Sorry . . .should have expanded on my thoughts. | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 111 Registered: 8-2003 |
Thanks folks for your responses which I am fairly confident hit the mark. I think the young chap attempted to move the vehicle to make the boot more accessible. In doing so he used the jumper leads that were stored therein to connect the new battery to the old and got the +/- the wrong way round. The leads were not exactly where I always leave them and the car didn't get moved. Obviously the car did not start. Ultimately he managed, with what would have been some effort, to install the new battery which was connected correctly when I got to it. Now I have to work out how to repair the damage. Auto electronics is not something am at all good at and there is no-one within 600 kilometers I would want to undertake the task, so I will have to have a crack at it myself. I would be most grateful for any advice on the steps I should be taking to check the problem and undertake repairs. I have all the manuals and tools (I think) to do the job but not the technical experience in the area. Thanks in anticipation. Peter | ||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 1873 Registered: 6-2006 |
 To check you can bridge out the shunt and see if that restores power to everything. Next TIPEX a big + and - on the battery so it can be clearly seen. Two choices then really, Have a little hope that it is just the shunt and nothing else is damaged. 1 - You can replace the shunt and ammeter gauge . The shunt is on the bulkhead on the right hand side of the engine bay about 45cm in with Big Brown and Brown and white wires going to it. ( A shunt is about £185 A used gauge about £70) 2 - You can bridge out the shunt and fit a voltmeter in your 4 in 1 gauge instead. Not as tidy at the shunt but cheaper. A used gauge is about £70 (or choice 3 is I guess. Bridge it out and and not have any sort of charging gauge.) Have a read through the manual, Disconnect the battery before working on the shunt. Good luck, Paul. | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 112 Registered: 8-2003 |
Thanks for that Paul. It certainly gives me a starting point and at least I will get to know what the shunt thingy is about. Cheers Peter | ||
| Tim Millard Unregistered guest Posted From: 1.124.111.235 |
I bet polarity was reversed upon battery installation and it has blown the shunt and ammeter. (Message approved by david_gore) | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 113 Registered: 8-2003 |
Thanks once again to all for the input. Paul, am I correct in deducing that bridging the ammeter shunt is simply connecting the brown and white wires and the brown and brown wires to each other? If I do this and everything lights up and the car starts is there any risks to anything else electrical if I drive it to a suitable auto electrician to take a look at? This would take about 4 hours of driving. | ||
| michael vass Grand Master Username: mikebentleyturbo2 Post Number: 375 Registered: 7-2015 |
Hi peter I would connect the wires using a wire with a fuse in it 20 or30A just to see if power is restored, if there is a short anywhere you won't burn anything OK Mike | ||
| Patrick Lockyer. Grand Master Username: pat_lockyer Post Number: 1548 Registered: 9-2004 |
A 50 amp fuse will be needed if all is working as it should on start up. This will take care of the high charging amps on start up with a fast idle. | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 114 Registered: 8-2003 |
Thanks for that information, so glad I asked the question. Messing with auto electrics is not my forte' but have no choice but to give it a go. Cheers Peter | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 115 Registered: 8-2003 |
Hello again, made up some jump leads with 50 amp fuses. Pulled the female leads out of the shunt and connected them with the jump leads and reconnected the battery. Nothing happened other than I have lost the few bits and pieces that were lighting up before I started. Nothing at all now. The battery is reading 14.1. I am going to go through all the fuses again. Is there a logical number of points after the battery where I should test to find power? Thanks in anticipation. Peter | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 116 Registered: 8-2003 |
Just pushed the female leads back into the shunt and the lights I had before have come back on. Obviously I am doing something wrong. I connected the large brown lead from the shunt to the smaller brown lead with a jump lead. I did the same thing with the large and small brown and white leads. Is that correct? Thanks Peter | ||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 1879 Registered: 6-2006 |
Sorry. A message went missing. Bloody double click to post feature !! NB the gearshift actuator can also rotate to the wrong position. Keep your foot on the brake when starting in case it is in gear although it should not really start like that (let's cross that bridge if and when we get to it) They need to be jumbled and then put back onto their terminals on the shunt. Piggy backs would be best but I've never seen them that size (I've never looked for any though). To test or move a car from a difficult position I push the jumpers bare wires into the female terminal and then push them back in place. Never left it running like that for long though. Do you have AA recovery? In the UK you need to be half a mile from home to get it taken a long distance 10miles plus, to a garage of your choice. I get cars on recovery trucks from all over the UK . No idea how it works out there though. | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 117 Registered: 8-2003 |
Thanks for that Paul but I am a little confused about the "gear shift actuator" thing and the term "jumbled". We do have something like the AA here but I only have our daily drivers covered not the Rolls. Either way our RACV doesn't offer anything as good as what you are talking about. Cheers Peter | ||
| Martin Taylor Frequent User Username: martin_taylor Post Number: 90 Registered: 7-2013 |
Does your car have a battery isolator switch in the boot? Check this because if installed by a pro it will leave the clock and interior circuits live (so you don’t have to reset the time) and all other circuits dead. Otherwise check for 12v with a test lamp or similar loaded device at the starter solenoid and then relays. The battery ground strap can also fail where it connects to the body if there is a massive surge etc | ||
| ross kowalski Grand Master Username: cdfpw Post Number: 576 Registered: 11-2015 |
Peter, No idea what's actually wrong there but it sounds like the Royce needs a date with the test light. I don't know your adventure quotient, ... but if your car is points and the shifting kit is functioning you would seem to be two wires away from driving to the shop. Be sure to brush up on your hand signals before the trip. | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 118 Registered: 8-2003 |
Thanks Martin & Ross The car has an isolator switch in the boot in the form of a brass wing nut that bolts the negative battery cable to the car body. When disconnected it turns all power off. It is always disconnected when the car is not in use (which is most of the time) and the battery is placed in a low charge situation. When connected only dim interior lights are on. If the ignition is turned on there are no instrument or ignition lights but when the auto transmission lever is moved the switch can be heard to click through each position. I will try to do some more testing as suggested today and hope for the best. I might try to remove and inspect the ammeter shunt which is really difficult to reach and/or see where it is, though I am not sure what that would achieve in view of the fact that the jump test I did didn’t show anything. Cheers Peter | ||
| Martin Taylor Frequent User Username: martin_taylor Post Number: 91 Registered: 7-2013 |
Before you take anything out ( and potentially create more problems as wires like to fall off things when you are in there) get a test light on the starter, bigger bulb the better to load it up. The battery feeds the starter, from there it goes to the starter relay and fuse box. Make sure your battery ground is ok and that the ign fuse is ok, also press the button on the thermal cutout. Rereading you postings and it appears when you bridged the shunt things got worse and less worked, this would indicate a poor connection somewhere and the voltage dropping away when load is increased, leave the shunt bridges and for voltage to earth, common failure points are Battery connection to ground in boot, Battery connection to starter from large lug to small lug to fuse box feed, Starter relay connections or crimp connections inside lugs at battery or starter relay. A headlamp bulb would be an ideal feast light for a high current circuit | ||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 1881 Registered: 6-2006 |
Sorry . . .jumped . . .not jumbled. Push the bare ends of a wire into the two big wireterminals and then push the big wires back on to their connectors. You need to get power from the left side to the right side so all four wires are live. Don't worry about the gearshift for the moment. | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 119 Registered: 8-2003 |
So what I did was incorrect in joining same colour large and small wires/connectors. I need to join large brown and large brown and white wires with a single wire and slide them back onto the male terminals? Do I need to have a fuse in that wire? Thanks Peter | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 120 Registered: 8-2003 |
The location of the shunt makes it difficult to see and work on. I made up a jump lead with a 50A fuse link in it and small crocodile clips on the ends. By feel I think I was able to attach them to the large male tabs in the unit. I left the small shunt wires in place. When I connected the battery there was nothing live at all. I replaced the proper wires and the dim interior light were on again and the gear lever switch clicked when it was moved. I am going to look at the manual to see how to remove the air conditioner fan padded cover ETC so I can and make sure I am making proper contact with the terminals with the jump lead and try again. At a glance it doesn't look too easy. Sorry to everyone for this issue becoming a bigger production than Gone With Wind but you folks are the only accessible source of knowledgeable information I have. Cheers Peter | ||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 1884 Registered: 6-2006 |
Hi Peter, have you got a test light with a spike? The bridging excercise was supposed to be a quick 5 min test first to see if that was the problem. A diagnostic step mainly. A thin wire to bridge the two thick terminals to start with is fine. See if power is restored first. If you have one Stick your test light in all four connectors and see if they are all live or not. Just checking. Have you swapped the fuses around? Or tested both ends with a test light? Not just visually checked them? | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 121 Registered: 8-2003 |
Hello Paul, yes I have a tester it is a brass pointed thing with a built in light and has a thin wire with another pointing device at the end of it. I will do as you say first thing in the morning. I was going to individually test all the fuses today but it became too late in the day and the temperature in the shed was about 40c so I will do that tomorrow too. Many thanks for your time Paul it is truly appreciated. Cheers Peter | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 122 Registered: 8-2003 |
Hello again, I have multimetered all fuses in the fuse box and the only one that appears faulty is 21 Windscreen wiper and washer. The only power I could find at the shunt is from the large plain brown wire on the right of the shunt when looking from the front. It was reading 14.14 volts. Guess/hope this means something? Cheer Peter | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 123 Registered: 8-2003 |
I should have mentioned with all 4 wires from the shunt taken out there is no power anywhere. When they are replaced the bit of power to the interior of the car comes back on. There are no external lights at all but when the hazard switch is pushed on the flasher unit (without lights)operates and as it clicks on and off the bit of light goes from dim to dimmer and back. | ||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 1892 Registered: 6-2006 |
Peter, get a normal size piece of wire and bare the ends. Push the ends it into each of the large female connectors. Push the connectors back onto the shunt. Let us know what happens. Cheers, Paul | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 124 Registered: 8-2003 |
Did what you said. Side light came on but no head lights. Ignition light comes on briefly and the speedo needle rotates up to about 80 then slowly drops. Ignition light stays on when key turned to acc. Hazard light dimly working. Interior lights come on but dim when something else is turned on. I will look for more shortly but wanted to let you know this bit ASAP. Cheers Peter | ||
| ross kowalski Grand Master Username: cdfpw Post Number: 578 Registered: 11-2015 |
Peter, Did you unhook the battery cables and read the resistance across the leads? | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 125 Registered: 8-2003 |
No I had not. I have tried to now but the only reading I can get is 1.8 to 1.9 at a 200 ohms. I am not sure I have done this right and no idea what I should expect. I only received the multimeter last week and it arrived without instruction so I am no wizard on the subject. The other scales on the meter are 20k 200k and 20m. The only one that would read anything was the 200. And yes I am chasing the supplier for the instruction book. Hope that is what is needed. Cheers Peter | ||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 1896 Registered: 6-2006 |
It the battery flat now ? Is the battery definately fitted the tight way ? Did the jump wire feel warm? | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 126 Registered: 8-2003 |
Hi, the battery is showing 14.16V and is negative to earth. There is no heat in the jump lead. Every time I connect the battery to do another test there is a bit of difference in what does or not come on. Most of the time when power is on there is that tiny buzzing noise in the vicinity of the dash behind the brake pressure lights (I think). Turning the key to ‘Run’ the speedo needle rotates to 100kpm but everything else goes off. After 3 to 4 tuns it reduces in rotation at each turn on, to zero. Turning the key to ‘Off the lights etc, come back on but still dim. Turning the key to just touching ‘Start’ without a full turn, all the dim lights go even dimmer. Any increased pull on the power i.e. moving the transmission lever, opening and closing a door temporarily stops the dash noise. Noise also stops when the key is turned to ‘ACC’ and the generator light comes on. One crazy situation methinks. Peter | ||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 1898 Registered: 6-2006 |
It's tricky but if you are getting more systems by bridging the shunt I personally would still be pursuing a reversed battery situation. This can lead to lots of random problems with damaged diodes etc. The speedo jumping up often happens when there is low voltage. I would probably check the big battery cable at the starter motor next. There is a spring washer under the nut that can rust or burn out. Shame you're not closer. Actually . . . with the weather here . . .Shame I'm not closer :D | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 127 Registered: 8-2003 |
Paul, thanks for that. I will act accordingly. I am sure the battery is in the right way round though. Wish you were here too. I am English, born and raised in Blackpool. I agree with you about the UK weather. I love the Aussie heat but my wife who is an Aussie would kill to live in the the UK. If you should be out this way any time, drop in. I will buy you a beer. Regards Peter | ||
| ross kowalski Grand Master Username: cdfpw Post Number: 582 Registered: 11-2015 |
Peter, 1.8ohms is high. I don't even remember the last time I did this test on anything, but 1.8 ohms is like 6 amps. That would drain your battery overnight. Your car is old enough that there shouldn't be a lot going on when the switch is off. I think some diodes are definitely bad or there is a short or something. I don't know what the load should be, but in the kohm range anyway I would think. If the rain stops here I'll check on my car and get you a number. | ||
| ross kowalski Grand Master Username: cdfpw Post Number: 585 Registered: 11-2015 |
Peter, I just pulled the wing nut and tested through the frame and the positive terminal on the battery. I pulled the wire from the boot light to get a more accurate baseline. SRH 8824 measured 9 M ohms which is basically no connection at all so 1.8 is high. | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 128 Registered: 8-2003 |
Many thanks for that Ross. You are communicating on issues that are on the edge of my limited auto-electrical technical knowledge and capability. I will however endeavor gain a better understanding and make use of your information. Firstly I will replicate the test you did on your car and see what I can come up with. My battery is always disconnected and place on trickle charge when the car is not in use. Is it possible for a new battery to be reverse charged resulting in reversed polarity? If that sounds stupid just accept it as a statement confirming my limited knowledge of the subject matter. Cheers Peter | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 129 Registered: 8-2003 |
Ross, just to clarify the test you did. You connected the multimeter from the positive terminal of the battery to the body of the car where the wing nut screws on and then you tested again by connecting the live wire from the boot light to the same place still using the multimeter. Is that correct? Cheers Peter | ||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 1899 Registered: 6-2006 |
Peter, It is possible to charge a battery the wrong way round although it's not supposed to really. If you put your multimeter on the battery . Red to the + then it should just sat 12.5 or whatever. If you put the red on the - terminal, it should come up as -12.5 | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 130 Registered: 8-2003 |
Thanks for that Paul, I just tested it again and it is definitely not the battery. Still showing 14.13 V positive to positive and negative to negative and minus 14.13v when the test probes are reversed. Cheers Peter | ||
| ross kowalski Grand Master Username: cdfpw Post Number: 587 Registered: 11-2015 |
Peter, When you disconnect the battery, what you are doing is making sure that there isn't any electricity flowing through the car when it isn't being used. The idea there is to prolong the life of the battery charge. This is like infinite resistance (no connection whatsoever) Depending on how much resistance there is measured at the battery cables, that tells how much electricity will be "flowing" when the battery is hooked up. An ideal car would measure infinite which translates to no connection whatsoever, but in practice with leaky diodes and water and clocks etc you rarely have infinity (thought the 9 M ohms I measured is pretty close) When I did the test I unhooked the negative cable from the car chassis and measured from the chassis where the cable bolted on to the positive cable of the car (though attached the battery was not part of the measurement) Also, 1.8 ohms might be OK (though I doubt it) But that means 6.666 amps of current all the time. On a car battery with a 85 amp hour reserve capacity, 85 / 6.666 = 12.76 hours before the battery goes flat. | ||
| Martin Taylor Frequent User Username: martin_taylor Post Number: 92 Registered: 7-2013 |
Ross, with all due respect, your ohms test is kinda pointless, and to suggest it to a guy with limited electrical knowledge is quite probably more pointless, the 2v his ohm meter produces will not even measure a diode etc, and it will tell him nothing helpful if it does, the boot light will also be in circuit in this test as that has to be open. May I suggest a more methodical approach. Step one, verify the battery is good by connecting a load to it, measuring voltage is useless unless there is a load present. Connect a headlight bulb or similar across the battery. It should light, if not replace battery. If it lights, next connect it between the positive of the battery and a ground point away from the battery, if it lights your ground circuit is ok (for 5 amps at least), if it does not light your ground connection is open circuit (this can be hidden as paint between washers etc will do this). If your ground circuit is ok check for power at the big terminal on the starter (other connection to ground), if it lights your main feed circuit is ok, if it doesn’t there is an open circuit between the positive terminal and the starter.. Leave the shunt bridged. Check for power at the shunt next, if it lights you have it, if not you have an open circuit. Get back to us here for more steps after doing the above. | ||
| ross kowalski Grand Master Username: cdfpw Post Number: 593 Registered: 11-2015 |
Martin, The meter doesn't need to meter diodes, it just needs to see that a diode is shorted. Lose an alternator diode and the battery has a path to earth through two of the alternator stator coils in series...1.5 ohms maybe. | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 131 Registered: 8-2003 |
Hello all. Many thanks for your ongoing attempts to assist me. Martin has elevated me from my extremely sub-limited status to “Limited” I truly wish I rated such an honor. The only reason I am trying to do what I am is because of the current status of the vehicle (immobile) an my remote geographic location. If there was anyone in my area who was suitably qualified to work on the car they would already be doing it. As I was not 100% sure I had actually bridge the shunt due to its extremely difficult location I undertook steps 4 to 9 Fan Duct Removal. A simple task as long as you move a few other bits and use brute force to extract the unit. Anyway the jump lead was in place after all. Due to the position of the car in my shed I am unable to get a jack and stands under it at this time to work on the connection that need to be checked underneath. Pity really because it is only 8 feet away from my 4 ton 4 post hoist on which it usually spends its time. Eventually I will get some help to push it outside to work on. I did some of the testing suggested using 12V handheld spotlight. • Positive to Negative battery test with no battery leads connected to terminals Full light. • Light positive connected to positive terminal, light negative to body earth. No light. • At one point with the light Positive connected to the Positive terminal I accidentally caught the test lamp negative on the battery hold down cradle hook nut and the light came on. When I touched the negative to the bare metal around the wing not hole nothing happened. Not sure what I have to test on the shunt while the bridge is in place. Is it the female plugs or male tabs or both. The bridge is just bare wire ends poked in the large female wire end and pushed onto the matching male tabs in the unit. I have not attempted to remove the shunt from its poison on the bulkhead as yet or to open it to see what it looks like inside. Should I? Sorry to ramble on folks. I will run the tests again tomorrow. Cheers Peter | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 132 Registered: 8-2003 |
Back again. Just took another quick look at the battery to work out why the light came on when I caught the nut on the cradle with the lamp lead. Turns out that the metal battery frame that holds the battery down and in place was hard up against the negative terminal and was shorting to the body through the hook. I moved it and the light doesn't come on any more. I think it must have happened when the new battery was put in. Could this have been the cause of my problems. Cheers Peter | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 133 Registered: 8-2003 |
Sorry, just ignore the last post. I guess that negative short is much the same connecting the cut off lead with the wing nut. Peter | ||
| Martin Taylor Frequent User Username: martin_taylor Post Number: 93 Registered: 7-2013 |
Peter, you are making good progress! The battery needs to be connected for the tests above. Hook it up and test again, keep that hold down well clear of the positive terminal or things could get ugly! From what you describe you have a poor connection somewhere, if there was a short you would know from the large current when you connect the battery. | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 134 Registered: 8-2003 |
Thanks Martin, I will go through every thing I can again. I really don't have an understanding of the shunt and the power in and out aspect. I can not find a graphic of it but have seen Google images which shows wires going into the top and what looks like male tabs underneath. I have not attempted to remove it from the bulkhead to have a look at it, concerned that by doing so I may do more harm than good. I assume if I remove the two securing screws that will both release it from its fixed position but also allow me to look inside and see any damage. Would that be correct? Cheers Peter | ||
| Martin Taylor Frequent User Username: martin_taylor Post Number: 94 Registered: 7-2013 |
http://www.flyingspares.com/shop/rolls-royce-bentley-shadow-t1-t2-corniche-mpw/electrical/battery/ammeter-shunt-ud18802.html That is the gimage of the shunt, It’s function is to pass all vehicle current (excluding the starter motor) and provide a small resistance, this resistance then produces a voltage which drives the ammeter. Because it is a resistor it will get hot if the current exceeds the 60amps it expects to measure if the voltage is reversed for instance. When it gets hot it then acts like a fuse and melts. If that is your problem then a piece of wire connecting the two ends together will feed the circuits and all will work well with the exception of the ammeter.. The two small wires in the picture go to the ammeter, you could connect these together if that is the side you can get too. Or test and prove that is your fault first with your test lamp. Power at one side only and your link is blown, Power at both ends and your problem is elsewhere. All testing is done with one lead to ground and with the battery connected. If you decide to bridge the link (hopefully after testing) then disconnect the battery first. Bridge then carefully reconnect. | ||
| ross kowalski Grand Master Username: cdfpw Post Number: 595 Registered: 11-2015 |
Martin, Why does more current flow through the shunt when the polarity is reversed? Peter, If you already bridged the shunt and you have not mended the thing, it's possible the bridge is not thick enough. The shunt carries many amps so the wire doing the bridging should be as thick as you can get jammed in there. You can unhook all the wires from the shunt and measure the resistance across it (big terminal to big terminal). Infinity means burned out, low resistance (.something ohms) means working. Good Luck | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 135 Registered: 8-2003 |
Tests? & Observations!!! Battery in boot with shunt bridge in place. Lamp test from Positive to Negative with both terminals connected: Good. Lamp connected to Positive no leads on terminals, lamp negative connected to car body where the battery Negative usually connects: No light. Multimeter reading with both terminals connected: 10.69V. With only Positive connected: 13.77V. With both terminals disconnected: 13.85. The battery is due to go back onto trickle charge. In car: Battery connected. Observed from outside: Boot, interior, seat belt warning, fuse box, glove box and interior lights all dimly on but dimming further when the door is opened. Park lights turned on all interior light dim further. When parks are tuned off the interior lights recover at a brighter level. At a second test of the parks they came up much brighter and interiors did not dim further. Turning the headlights on turned everything else off. When they were turned off the interiors recovered to their dim status. The clock kept ticking through all procedures. Ignition switch turned to: ACC. Gen light comes on. Lock & Run all interior lights go off. Eventually when returned to Start the lights come on slowly but dim again. When opened the car door light temporarily dim the others further. No Gen or Oil light show through any of these checks. Shunt area: Battery fully connected. Bridge in place between the two large female connectors that were pressed onto the male tabs. Power was found at both terminals. Test of the large female connectors when removed from the bridge and male tabs resulted in power only at the Brown wire, nothing at the large brown and white wire. No power was found a either of the smaller female connectors. I guess if nothing else this shows the shunt has had its day. I would like to leave it bridged until the car can start and run again and fix it later. I have yet to have a go at fixing any poor earthing there may be. Is there a common list of the week point for this type of thing? I know some like the starter are under car which is a bit difficult just now. I am hoping to borrow winch, push the car out of the shed and winch it back in and onto the hoist. As always any comments and advice will be greatly appreciated. Cheers Peter | ||
| Martin Taylor Frequent User Username: martin_taylor Post Number: 95 Registered: 7-2013 |
Ross, the output rectifier on the alternator is a dead short to ground of the voltage is reversed (almost anyway as a forward conducting diode has a volt drop of 0.6v, when polarity is reversed you have three pairs of two diodes forward biased in the same direction. This does its best to reduce the 13.8v battery voltage to 1.2v, no ohms law required to calculate that it usually makes a bang and fortunately the ammeter shunt then becomes a fusible link and blows apart removing reversed voltage from the alternator output, most likely what has happened and if lucky the diodes are still good on the alternator. Peter, with your shunt bridged you now have the symptoms of a flat or dead battery (probably what started this game). Charge or connect another (observe polarity!) With it connected measure the voltage at the points above with a load on (lights etc) if you need to. | ||
| David Gore Moderator Username: david_gore Post Number: 2691 Registered: 4-2003 |
Peter, Martin is probably on the right track and I would not be surprised if you have current leakage through faulty/fused alternator diode[s]. I would try disconnecting and isolating the alternator output lead and, using the existing battery, repeat your interior light test. If the lights appear much brighter then the short is in the alternator. If they continue to dim as more lights are activated then the alternator may be eliminated as a cause but may have to be reconsidered if the battery charging voltage is not 13.5V or more when the engine is running. If the alternator is found to be the problem and an auto electrician is located within the range of the car operating on battery power with no alternator input, make sure the alternator output cable is fully insulated and securely fixed in the engine bay and head for the workshop so they can fully diagnose and test your electrical system plus overhaul the alternator [I presume it is the CAV 85amp unit]. If you are of the "belt and braces" persuasion, have a second car accompany you in case of problems between home and the workshop. Electrical system gremlins are always a PITA to diagnose....................... | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 136 Registered: 8-2003 |
Thanks Gentlemen, will pursue your suggestion tomorrow. Cheers Peter | ||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 1901 Registered: 6-2006 |
Hi, I'm on my phone so only looked briefly at this. Do make sure the battery is fully charged. Now the thinner jump wire shows a positive result you can try to wedge a bigger wire in there. The fact that the thin wire is not getting warm points to no really heavy loads or short circuits being present at the moment. If you do try to move it remember you will have NO brakes. Also winching from the rear is tricky due to a lack of winch points. The car battery must be fully charged first. You can Also introduce an extra 12v feed at the shunt. With an extra battery. Put the black jump lead between the negative post and a good engine bay earth ( pas pump post, bonnet catch mechanism) Put a thicker wire into the dead shunt wire. Plig back into shumt. Along with the smaller bridge wire, then connect the thick wire to the positive post. This should give a direct feed to the cars circuit bypassing the starter motor. Test all systems and report back. Both batteries must be fully charged. Good luck. | ||
| ross kowalski Grand Master Username: cdfpw Post Number: 597 Registered: 11-2015 |
Peter, Is there any sort of respectable garage around your parts? Most garages will load test a battery for a nominal fee. Worth it to know you are at least working with good batteries. That would take the guessing out of that. You sound like you were pretty secure with the mechanical part of removing the parts to access the shunt. If you could pull the shunt you could see it melted in two. It sounds like pulling the shunt is a job, but at least it's just wrenching. Also, you could then post a picture of the thing and it's location in the car. Martin, Hoping for Peter's sake it's the shunt but it's hard to believe the diodes are OK with whatever current melts a shunt. Also, too bad it didn't happen during next year's symposium we could have no end of fun with test leads and lights. | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 137 Registered: 8-2003 |
Thanks for that Ross. In almost 60years of driving I can not recall a brand new battery failing. Using my limited equipment and skills it looks OK to me but I will as you suggest be taking it back to the original place of purchase for professional load testing. Paul: The jump wire I used was a single piece of 240V cut from a 3 core extension lead, much larger than normal car electrics. If I do winch the car onto the hoist I will be pulling it very slowly on forwards moving wooden blocks along in front and behind as we go. It will not be going anywhere of its own volition. At this stage the task is still in the "IF" folder and may not happen. I gave up rolling around on the floor under cars on my 65th birthday ten years ago and bought myself hoist as a present, but its beginning to look like a hands, knees, jack and, back job may be the preferred option this time. Que Sera Sera; Cheers Peter | ||
| Martin Taylor Frequent User Username: martin_taylor Post Number: 97 Registered: 7-2013 |
Test the battery voltage with load first, interior lights and headlights should be enough. See what your volt meter reads. If below 11.5 jump start it with another battery or car and you should get moving. Many years ago I took my car for a warrant of fitness inspection, it passed, I happily returned home and reversed it into my rather small garage and went about my day. At about three in the morning I was awoken by a banging on my door, I stepped out of my bedroom (stark naked) to see what the fuss was about, my neighbour was at my unlocked front door, upon seeing the light he opened it! We passed a few moments of awkwardness and I grabbed a robe from my bedroom, he then told me one of my car alarms keeps going off. My house is above the street level where the garage is, his house is opposite. No problem, I’ll sort it, I grabbed the remote and headed down the stairs, opened the garage door to a sick sounding alarm, with dimly flashing hazards and the interior light dimly lit. The vehicle tester had pulled on the headlight switch when testing the lights and I hadn’t noticed it in daylight. I then tried the remote and it wouldn’t disarm because the battery was too flat! The alarm was also much louder with the garage door open. At this point I’m now regretting reversing the car into the garage, my garage is rather tight and there are shelves above the boot giving very little room (can’t open it fully and the car is against the back wall. So amongst the flashing lights and disorienting siren I open the boot and sling in my battery powered jump starter through the gap, I open the battery cover and back handed in dim light I connect up the jump starter, the resulting bang causes me to hit my head on the boot lid, the battery took most of the load and the siren stopped for 5 seconds only to start again. After some well chosen words I connected the battery the correct way and silenced the alarm. Peace at last I reached in and disconnected the battery negative cable. The shunt and alternator survived, the memory wire to the radio did not fare as well, this blew the fuse but also destroyed the input to the radio (later repaired). The battery never recovered. Lessons learned. Check the interior lights are off! Lock the front door! Always connect one end of the jump starter to ground and not the battery! Wake up fully before attempting repairs! | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 138 Registered: 8-2003 |
Martin, I undertook the following tests before taking the battery currently in use to be tested by the original supplier. Test Current Battery: 1. with no leads attached. Result: 14.4 2. only Positive attached. Result : 14.5V 3. with both leads attached Result: 14.4V 4. headlights on. By the time I got back to the boot to see what was happening the volt meter showed the battery power reducing at a rate of about 1.5V per second. I disconnected the battery, repeated the test with the same result. I removed the current battery and replaced it with my spare which is used primary as a backup carried in the boot for emergencies (I once had a flat battery at a friends wedding and never quite got over it.) Test Back Up Battery: 1. with no leads connected. Result: 13.91V 2. only Positive attached. Result : 14.87V 3. with both leads attached. Result: 13.68V 4. headlight on. All lights came on full bore. I was absolutely stunned. I turned them off and on again, same result. I checked the engine bay to ensure I had not left too much hanging around that could damage or be damaged and turned the ignition key and the starter turned the engine. I only let it do two turns as I didn’t want the engine to actually fire at that time. So there you have it looks like it was the battery as was said. Its Friday 13th so I was not game to push my luck further today and will put the old girl back together tomorrow. I am Assuming under the circumstances the shunt might be OK and I can remove the bridge. I can not believe that it has taken over 60 posts on the Forum to get to this point, predominantly because of my ignorance and inability to understand clearly what the talented members attempted to tell me. Any further comments on the subject would be very welcome and hopefully some time tomorrow I will make my last post on this issue by confirming all is well. If all is not well I will not need to post the fact because you will hear me scream. Salutations to all, Peter | ||
| richard george yeaman Grand Master Username: richyrich Post Number: 849 Registered: 4-2012 |
The real lessen here is not to have someone mess with your car in your absence, your next problem is trying to extract your money from your battery supplier......good luck on that. Richard. | ||
| Patrick Lockyer. Grand Master Username: pat_lockyer Post Number: 1566 Registered: 9-2004 |
I always check out the battery first with these with any electrical failings.  | ||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 1903 Registered: 6-2006 |
A great step forward. I'm hoping that was all it was. https://www.facebook.com/BentleyWales/videos/1482861581750009/ Wish I hadn't bothered blowing up a car and crawling upside down through the dashboard to make this video especially for you!! Good Luck with the next stage, really hoping that it was just a faulty battery or . . .and some do . . .the new one just hadn't been charged after sitting for a while :D (I didn't just take the video, I knew it was somewhere on my computer . . just did a search through all the photos I take but never get around to sorting out. LOL. ) | ||
| Martin Taylor Frequent User Username: martin_taylor Post Number: 98 Registered: 7-2013 |
Well done Peter, From your test results your ammeter shunt is still open circuit. A secure bridge will have the car back to normal with the exception of the ammmeter, to get you running at least. Any door not closed or light left on will kill a battery in a few days if not hours these cars | ||
| Martin Taylor Frequent User Username: martin_taylor Post Number: 99 Registered: 7-2013 |
You will need to start the car and see if your alternator is working, do this with your volt meter across the battery with the headlights on at fast idle. It will most likely be ok but best to know before taking the car out. Volt meter should read above 13.5 | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 139 Registered: 8-2003 |
Hello, just going through the process of confirming the shunt is US by removing the jump wire. Result no headlights without it. Reconnected jump wire full lights come on. This was done with the backup battery I have showing 13.4V. The other battery is/was definitely dead and will be replaced under warranty by the supplier. I am about to order another shunt probably from Flying Spares. Was wondering about using a used part instead of new. Has anybody any knowledge of anyone using this type of used part and any adverse outcomes? Martin thanks for that I will undertake the alternator test as suggested. Cheers Peter | ||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 1904 Registered: 6-2006 |
OuCH! A good used one should be OK. But not all that you will need. Drop me an email and I'll give another suggestion. | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 140 Registered: 8-2003 |
And she came alive and gave forth with a mighty roar at the first turn of the key and I withdrew the many curses I had cast upon her and forgave her all her sins. Halle bloody lujah. Thanks to everybody for all the input and help Cheers Peter | ||
| ross kowalski Grand Master Username: cdfpw Post Number: 600 Registered: 11-2015 |
Peter, What's the voltage across the battery when running? The part about not believing a new battery could be bad because it never happened in 60 years reminded me of a story. A few years back I was diagnosing a short from a computer to ground. A couple of techs (literally rocket scientists) were trying to figure it out when I arrived. They had unhooked the wires and were still getting the short. I pulled out my meter and measured it out and told them it was shorting through the wood the computer was mounted on. They told me that it was impossible and the even if the wood could conduct electricity it certainly could not conduct any appreciable amount of current to signal a gpio , etc, etc. I said something like " I doesn't sound very likely to me either, ... but the meter says it's the wood." After a bunch more talking the computer was insulated from the wood and the short stopped and everything worked fine again...because it was the wood. It was a good lesson for them, don't accept anything but what you have tested, and if the meter says it's the wood.... | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 141 Registered: 8-2003 |
Martin, Ross and all. At revs slightly higher than idle Volts across the battery read 14.6. Is that good or bad? Thanks Peter | ||
| David Gore Moderator Username: david_gore Post Number: 2697 Registered: 4-2003 |
Perfect - 14.9+ volts is straining the friendship because out-gassing occurs resulting in loss of electrolyte in the cells as the water content breaks down into oxygen and hydrogen increasing the Sulphuric Acid concentration which accelerates formation of Lead Sulphate deposits on the lead plates and consequent loss of capacity to deliver the rated current on discharge. | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 142 Registered: 8-2003 |
Thanks for that David. I would love to be able to say I already thought all that, but of course I really didn't have a clue. Which direction is 14.9V "straining"? Too much or too little charge. I realise that I should probably be able to deduce the answer from what you have said but I am just not up to speed with the science of this stuff. Cheers Peter | ||
| Martin Taylor Frequent User Username: martin_taylor Post Number: 100 Registered: 7-2013 |
Your alternator is charging, hopefully on all three phases, you will find out in time, the regulator has three terminals on it for low medium and high, sounds like yours is set to high. 13.6 v normal healthy charge 14.4 v charge voltage for modern calcium batteries. 14.7 is a little high, or your meter could be cheap junk giving a less than accurate reading. Or your car could have been riunning like this for years. Good that it is charging  Find a used shunt, if it is in one piece it is as good as a new one. Or bridge it permanently and fit a voltmeter rather than ammeter. | ||
| David Gore Moderator Username: david_gore Post Number: 2698 Registered: 4-2003 |
Peter, 14.9 Volts is the absolute maximum for charging a 12V battery due to the outgasssing problem I described above. Always best to ask for more information/explanation if you are not sure as you did in this instance. We are always understanding in this situation as we have all been in similar situations ourselves in the past. | ||
| Martin Taylor Prolific User Username: martin_taylor Post Number: 101 Registered: 7-2013 |
http://www.ebay.ie/itm/ROLLS-ROYCE-SILVER-SHADOW-II-AMMETER-SHUNT-CABLE-P-N-UD18802-/272836095538?hash=item3f864c6e32:g:55cAAOSw0AxZlY~P | ||
| Peter Dixon Prolific User Username: petenlinid Post Number: 143 Registered: 8-2003 |
Thanks to all of you. Martin, how and where is a voltmeter fitted? I would want to make a better bridge than just bared wires stuffed in the connections. Though my leaning is towards a shunt replacement I can be tempted by economics if the difference is large enough. Cheers Peter | ||
| Martin Taylor Prolific User Username: martin_taylor Post Number: 102 Registered: 7-2013 |
The shunt is only there to run the ammeter, a few spade connectors and a short piece of wire and it’s removed from the equation. A voltmeter can be fitted in place of the ammeter and will tell you as much useful information as the ammeter did. A volt meter simply needs ign switched power and lighting to light the gauge. My car has a coolant gauge fitted in place of the ammeter in this manner. However with your limited electrical knowledge it may be easier to replace or bridge the shunt. Working in the dashboard can be harder than it seems as it is easy to knock wires off unrelated components and make further headaches. Remember most modern cars only have a warning lamp. | ||
| Jeff McCarthy Grand Master Username: jefmac2003 Post Number: 538 Registered: 5-2007 |
Rather than start a new thread I think my question more usefully belongs here. Today I physically broke my ammeter shunt trying to remove the corroded terminals for cleaning. I don't have the ammeter - I replaced it with a Coolant gauge. I need to bridge the circuit. Questions: 1: Brown/White to Brown/White And Brown to Brown - Yes or No ? Or is it Large Wire to Large Wire (and Small to Small or not at all? 2. Using a dremel I shaped the manganin bits of the shunt to connect the female to female terminals (like a large version of those 6.3mm metal bits for connecting 2 female lucar terminals that are all over the car). Is this OK? Do I need to fuse this? I won't be starting the car until I can fix this or get a new Shunt? (The exposed manganin in between the terminal ends is covered in 2x double walled heatshrink) I also have Voltmeter installed in a pod below the dash. | ||
| Jeff McCarthy Grand Master Username: jefmac2003 Post Number: 539 Registered: 5-2007 |
Just further to this, If the manganin is not an acceptable connector what size wire and male connectors should I get to do the bridging? | ||
| John Kilkenny Prolific User Username: john_kilkenny Post Number: 294 Registered: 6-2005 |
Jeff, The shunt is in the circuit to provide a small voltage drop for operating the ammeter. As long as the shunt is replaced by a connector with at least the same current carrying capacity as the existing circuit you will be OK. | ||
| Jeff McCarthy Grand Master Username: jefmac2003 Post Number: 540 Registered: 5-2007 |
Thanks John. I'm still a bit confused about the wiring though. I assume I connect the big Brown wire to the big Brown/White wire (both cotton covered). There are 2 more smaller wires of the same colours (cotton covered) on the other side of the shunt. There are also in my car 2 Plastic wires of the same colours that went to the Ammeter. I don't know if somebody did a bodge at some point in history but researching RR ammeter shunts my 1974 car seems to have an older design that was supposedely deleted at about SRH8000; my car is SRH20280. And the wiring diagram shows no plastic wires at all. What do I do with the 2 smaller wires? Connect them/ Leave them unconnected? Maybe tomorrow I'll try and take some photos but it's difficult to get a camera in that part of the dash. | ||
| John Kilkenny Prolific User Username: john_kilkenny Post Number: 295 Registered: 6-2005 |
Jeff, According to both the 1973 and 1975 Specs the three Brown/White wires on one side of the shunt go to the Alternator output, the Switchbox and the Ammeter +ve input. The three Brown wires on the other side go to the battery +ve terminal, the Ammeter -ve input, the Gearchange Cutout and various fuses. If you disconnect the wires to the Ammeter you can connect all the others together. | ||
| Jeff McCarthy Grand Master Username: jefmac2003 Post Number: 541 Registered: 5-2007 |
Thanks for your help John. I've disconnected the Ammeter and removed those two wires. Of the four wires left I just need to understand: IF I connect 1-Large Brown (always live unfused from the battery) to the Large Brown/White wire. AND 2-Small Brown (always live?) to the Small Brown/White wire. OR 3- Connect the same colour to the same colour. | ||
| John Kilkenny Prolific User Username: john_kilkenny Post Number: 296 Registered: 6-2005 |
Jeff, The wiring diagram indicates that the large and the small brown/white wires are joined inside the shunt assembly. The same applies to the large and small brown wires. This means that if you join the large brown/white and brown wires (your number 1 above)you should see 12 volts on all four wires. If not you will need to do some wire tracing. | ||
| Jeff McCarthy Grand Master Username: jefmac2003 Post Number: 542 Registered: 5-2007 |
Right - that makes sense. It was the way I was reading the Theoretical Wiring Diagram but for some reason just couldn't get my head around what I was seeing in front of me. Also the possible consequences of doing it wrong and then connecting the battery may well be none - but then they might be anything from dead diodes to fire. I'll do the Large to Large and Small to Small opposite colour tomorrow and see if I get 12v live on all four wires - or even just check that the 2 Brown are always live which is the same thing. It makes sense from the basic Lucas colour coding that current would flow from single colour -> colour plus secondary stripe as well. Thanks again for taking the time to try and explain it to me. In the process, as frustrating as breaking the thing was, I've been able to get in behind the dash and clean up a lot of wiring that's come out of the looms or been twisted and chopped over the years; and get rid of that redundant Power Window Relay that made getting your hand anywhere halfway useful nearly impossible! | ||
| Jeff McCarthy Grand Master Username: jefmac2003 Post Number: 543 Registered: 5-2007 |
Last night I must have been befuddled from being upside down in the footwell all day when I wrote the above. The connections are same colour = same colour. To do otherwise would be the equivalent of connecting the battery the wrong way. So Large Brown Cotton to Small Brown cotton and Large Brown/White to Small Brown/White. | ||
| Martin Taylor Prolific User Username: martin_taylor Post Number: 143 Registered: 7-2013 |
All true, wires can be connected together and everything will work. However I wouldn’t. The Ammeter shunt often acts as a fusible link on these cars when someone does something unpredictable to the battery circuit. When it melts it can isolate the energy and save a car from a fire. If you chose not to replace it I would leave the wiring that used to feed the ammeter disconnected, these are not fused and if they touch ground they will cause a fire. Tape is not an acceptable solution as it fails over time and falls off and should never be used unless a short term emergency fix. The safest way forward may be to replace the damaged shunt with an 80amp fuse or fusible link. Connect whatever is still being used the same ends as it previously was. That way if someone ever hooks up a jump starter in the reverse direction the link will blow due to the 1.2v drop across the rectifier diodes in the Altenator and the current will not exceed 80 amps (your alternator will be saved). | ||
| Jeff McCarthy Grand Master Username: jefmac2003 Post Number: 544 Registered: 5-2007 |
Thanks for that Martin - important advice. And a solution. I assumed half the car wouldn't have power if the wires weren't reconnected. Rather than pay the AU$400 (plus tax plus delivery) for a shunt I don't use, for about $20 a couple of these might even fit into the female connectors already crimped on the wires?  https://www.autobarn.com.au/narva-fuse-link-plug-80amp-male-53180bl | ||
| John Kilkenny Prolific User Username: john_kilkenny Post Number: 297 Registered: 6-2005 |
Jeff, I'm not sure where you are now. If you connect Brown to Brown and Brown/White to Brown/White without the shunt you will have an open circuit and nothing will work. All four wires need to have 12 volts and the simplest way to take the shunt out of the circuit is to connect them all together. The only reason for having a shunt is to operate the ammeter (actually a galvanometer) . Replacing it with a 80 amp fuse is an option but one of the other fuses would most often blow first so it's probably a case of diminishing returns. | ||
| Jeff McCarthy Grand Master Username: jefmac2003 Post Number: 545 Registered: 5-2007 |
John, how do you mean "connect them all together" One of the wires is a double brown wire already in a large female connector. That means somehow connecting 5 largish wires into one connection. What would I use to achieve this? | ||
| Jeff McCarthy Grand Master Username: jefmac2003 Post Number: 546 Registered: 5-2007 |
Surely someone out there has bridged an Ammeter shunt before. Without explaining the whys and wherefores can you please tell us how to physically do this? | ||
| Jeff McCarthy Grand Master Username: jefmac2003 Post Number: 547 Registered: 5-2007 |
Maybe this? Rated for 300A https://www.ebay.com.au/itm/Heavy-Duty-4-Way-Bus-Bar-Power-Distribution-Box-Screw-Terminal-Studs-M8-5-16/401565727837?hash=item5d7f2ebc5  I have tested the wires with the battery connected. Only the Large Brown Cotton wire (which is 2 wires connected to the same female Lucar plug) has power from the battery. Unfortunately my multimeter battery died overnight so I can't test continuity at the moment. I'll have to go hunting for a new battery in town this afternoon. | ||
| Jeff McCarthy Grand Master Username: jefmac2003 Post Number: 548 Registered: 5-2007 |
It does occur to me that if I do this I will be sending power from the battery (Brown) to the Alternator output (Brown/White). Why does this seem to be illogical? | ||
| Martin Taylor Prolific User Username: martin_taylor Post Number: 145 Registered: 7-2013 |
John, You are correct, it is only there for the ammeter but will also act as a fuse if reverse voltage is applied, although it is clearly not a fuse. Cars of this vintage have no other fusing, so if there is a problem there is no protection, the energy from a battery is in excess of 600amps limited only by the impedance or resistance of the copper cables. Hence if you are removing something that although not primarily designed to offer protection effectively does, then it would be wise to replace with something to reduce future risk with elderly wiring, rarely used cars that are often jump or boost started more often than any other car due to their nature and usage. | ||
| Martin Taylor Prolific User Username: martin_taylor Post Number: 146 Registered: 7-2013 |
Jeff, Connecting the battery to the alternator is how the alternator charges the battery, connect the wires anyway you can to the fuse but make sure your connectors are good for 80 odd amps. It is often easier to drill and use a nut and bolt and stack any extra terminals on the bolts on either side as a tight nut and bolt will give an elxcellent low resistance connection and will not come loose. Spade connectors on a fuse can work but must be sprung tight or they will heat. | ||
| John Kilkenny Prolific User Username: john_kilkenny Post Number: 298 Registered: 6-2005 |
Jeff, Looking at the wiring diagram, the double brown wire you mention seems to go to the regulator control input as well as the battery positive terminal. The bus bar you show would be OK for joining the wires though 300A is probably an overkill. To answer your second question. It is quite normal to connect the alternator this way. The alternator diodes prevent the battery from discharging through the alternator. | ||
| Jeff McCarthy Grand Master Username: jefmac2003 Post Number: 549 Registered: 5-2007 |
You're right Martin - I just didn't realise that this was where the connection between the battery and the alternator was physically located. I have ordered a marine grade 2 pole Bus Bar with 3/8th bolt down terminal studs rated at 600 Amps at 48 Volts- this will allow me to connect all 5 wires with crimped and soldered heavy duty ring terminals and an 80A fuse between the Battery live and the Bus bar. It won't come loose. I own a very heavy duty set of jump starter cables with a black box in the middle which prevents any connection unless the following conditions are met: correct connection on all four clamps and motor running on donor car. This also has an spike damper and internal fuse. I keep it in the spare wheel with the tire upside down and can just squeeze it out through the boot access hole. I also have thick red and black covers on the battery terminals as a hint to anybody trying to connect the battery the wrong way round - but I do take your point about extra safety in case of worst case scenarios. |
