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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 1096
Registered: 5-2012
Posted on Friday, 11 March, 2016 - 03:39 pm:   Edit PostDelete PostView Post/Check IP

The brake lights on my car (74 SY1 - SRX18501) failed today. I took a quick look at the problem this evening and by luck found it was due to a wiring issue on the rear offside light cluster. I will investigate it further this weekend.

However, when the brake lights failed, the warning lamp on the dashboard did not illuminate. I really want to sort this in case the fault recurs.

My question is does anyone know how the warning light is wired to detect that the brake light bulb(s) have failed. A quick look at the wiring diagram appears to show the warning light only illuminates when the relay fails, not the lights. I may be wrong on this, as I only took a quick cursory look at the diagram.

If anyone knows the principle involved in how a failure on the braking lights is detected I'd be most grateful.

Geoff
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Paul Yorke
Grand Master
Username: paul_yorke

Post Number: 1471
Registered: 6-2006
Posted on Friday, 11 March, 2016 - 05:23 pm:   Edit PostDelete PostView Post/Check IP

Hi Geoff, it should work if a bulb goes or there is a bad connection at the lamp.

They can be a little sensitive, could somebody have disconnected it?

Your car may also have "brake light dimming' . These can play up and cause strange faults like the brake lights coming on with the side lights Or the hazard lights coming on when indicating but only when the side lights are on.

I have a feeling that the brake light warning only works if one light is faulty.

Good luck with her.
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John Kilkenny
Prolific User
Username: john_kilkenny

Post Number: 231
Registered: 6-2005
Posted on Saturday, 12 March, 2016 - 08:46 am:   Edit PostDelete PostView Post/Check IP

Geoff,
See Tee One Topics Issue 36, Page 526.
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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 1097
Registered: 5-2012
Posted on Saturday, 12 March, 2016 - 02:25 pm:   Edit PostDelete PostView Post/Check IP

Paul - many thanks. I will remove both bulbs this weekend to check if the warning light goes out, mainly out of curiosity.

John - It must be a matter of great frustration to you and Bill Coburn that people do not check tee-one topics before all else. This reminds me of my days in IT where the buzz word was rtfm - "read the flipping manual", where the word flipping could be upgraded, according to the level of annoyance.

It's a great diagram and explains all. It appears the later models used a single relay, judging from the respective wiring diagrams. This seems to be borne out by the fact I could not locate a relay near the one light cluster. I have not as yet removed the trim on the other cluster to investigate. In doing so this weekend I hope to find this relay.

It is clear that for the entire system to not work, as happened on my car i.e. no brake lights or warning light, the fault must be before or after the entire system. Since removing the light unit from the cluster has brought the brake lights back to life, it is most likely a faulty earth connection. I need only track this earth connection down and clean it up to prevent the fault happening again.

There is another curious thing happening. The stop/tail light unit uses a dual filament bulb, which we are all familiar with. There are two wires running into it, one for the tail light and the other for the stop light. Both filaments connect to earth though the metal casing of the holder. Why is it then that on my car the bulb continues to illuminate when the bulb holder is pulled from the light cluster, thus breaking the earth connection. Curious. I will no doubt figure this out this weekend.

brake light
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Paul Yorke
Grand Master
Username: paul_yorke

Post Number: 1472
Registered: 6-2006
Posted on Saturday, 12 March, 2016 - 04:18 pm:   Edit PostDelete PostView Post/Check IP

Another Brake light fault on Shadow 1s and earlier is an intermittent ļoss of both brake lights. No warning light.
Often works if you press much harder on the pedal the switch had moved away from the pedal.

(I hope this isn't in the Tee one you've just read, but knowing Bill it will be).

The switch is an ancient design using two wiper contacts on a brass plunger. The brass wipers have small ears on which do the work. These eventually wear through giving intermittent brake lights initially, very late bake lights, then no brake lights.

Confusing sometimes because they do not work whilst driving, but when testing the lights you often press the pedal much further (way past an emergency stop) so they then come on.

Don't know if that's your problem Geoff but I think it's worth a mention for others.



It's mounted in the rat trap.
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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 1099
Registered: 5-2012
Posted on Sunday, 13 March, 2016 - 03:38 am:   Edit PostDelete PostView Post/Check IP

Paul

I think you are right. There is quite an amount of travel on the brake pedal before the lights come on. I was hoping to get away with not having to remove the rat-trap cover, but I now know it was wishful thinking. At the very least I need to readjust the switch position.

It was just strange that everything started working again after I'd been playing with the rear light cluster. A red-herring I think. Much more likely to be an intermittent on the brake switch.

Geoff
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Robert Noel Reddington
Grand Master
Username: bob_uk

Post Number: 884
Registered: 5-2015
Posted on Tuesday, 15 March, 2016 - 06:18 am:   Edit PostDelete PostView Post/Check IP

On my Shadow I, near side boot bulkhead in the boot is a relay(s). Basically if a bulb blows the amps aren't present and this causes the relay to turn on the stop lamp failure. One set of contacts and coil for each bulb.

The brake switch in the rat trap is easy to repair and lasts well. The adjustment is via a cam which is unlocked then turned.

From long time ago memory the switch has a spring clip holding a cover on. My one had dirty contacts I used petrol to clean off the gunk. Polished up a bit with 120 grit.

The rat trap isn't difficult to remove just boring. Electric screw driver helps.
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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 1100
Registered: 5-2012
Posted on Tuesday, 15 March, 2016 - 08:29 am:   Edit PostDelete PostView Post/Check IP

Hi Bob

I pulled off the rat trap cover over the weekend and removed the stop lamp switch. Your memory is correct, the switch does have a spring clip cover. The contacts were fine and so I just gave it a clean and replaced it.

Then, a huge annoyance. A previous owner had obviously lost the adjustment cam and replaced it with a bolt. The head of the bolt was acting as the lever and had worn slightly - enough to take the brake lights out of adjustment.

I really wish people would not bodge these cars. I have ordered the new part (UR 12865) and locknut from FS - 15 quid. End of rant.

In fact, I'm going to have another rant. I wasted two hours of my day today, taking the drive from Tampa to Clearwater to have a replacement speedo cable made up at a specialist firm. When they saw the original, I took as a pattern, it was clear it was way beyond their capabilities. I just wish they had told me that over the phone and saved me the drive. FS will get my order tomorrow.

Geoff
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Robert Noel Reddington
Grand Master
Username: bob_uk

Post Number: 885
Registered: 5-2015
Posted on Tuesday, 15 March, 2016 - 10:05 am:   Edit PostDelete PostView Post/Check IP

Geoff,
I know the feeling and wish repairers would not lose these little bits which are not cheap plus it delays what is a simple job. It's frustrating.
Some times I have seen stuff left off because the mechanic can't be bothered to fit all the washers back its only a bracket for the handbrake cable sort of thing.
Also notice that a lot of the washers on a RR tend to be thicker than normal so maybe expensive to replace. Making them from stainless is an option. Bare mild steel will rust within days.
Worse is a wasted journey to some chancer who talks a good job but can't.

I had a Rover 216 with Ecu faults I called an expert out and he couldn't find the fault eventually I found no power to the memory of the Ecu.

I would have made a cam from a bit of steel.

The switch reminds of old Brit motorbikes. I like stuff like this because they are so easy to repair and robust in the first place.

I get a sense of satisfaction when I fixed a device especially if it costs nothing to repair. Smug mode.
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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 1101
Registered: 5-2012
Posted on Tuesday, 15 March, 2016 - 10:37 am:   Edit PostDelete PostView Post/Check IP

I would have made a cam from a bit of steel.

So would I, but unlike yourself, I don't have a lathe
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Robert Noel Reddington
Grand Master
Username: bob_uk

Post Number: 886
Registered: 5-2015
Posted on Wednesday, 16 March, 2016 - 07:18 am:   Edit PostDelete PostView Post/Check IP

I could just simply file one up. The accuracy isn't important just as long as the cam does the job.


Incidentally.

The stop tail bulb has 2 filaments with a common earth. If the earth is disconnected the 2 filaments are then in series using the the other bulb as an earth. Which why the bulb lights both filaments when removed from the light assembly. And also why the bulbs looks dimmer than normal. Also bad earths can cause indicators to work the stop tail bulb.

At first sight I wasn't impressed with the quality of the bulb holders and would like to see an earth directly fitted to the bulb holder. But mine are 42 years old and earth perfectly when fitted so I guess the quality is ok. Also the rear bulbs are at least 27 years old.

LED bulbs are available but because of the bulb failure circuit the LEDs will need a dummy load to keep the amps up. Which completely defeats the energy saving advantage of LEDs. The energy saving was very small any way.
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David Gore
Moderator
Username: david_gore

Post Number: 1941
Registered: 4-2003
Posted on Wednesday, 16 March, 2016 - 08:01 am:   Edit PostDelete PostView Post/Check IP

Bob,

I am under the impression the main justification for using LED replacements was their greatly increased service life compared to filament bulbs. Energy saving in a vehicle electrical system is a moot point given the low potential cost savings involved.

The lower heat output of LED bulbs is a bonus however their low current draw is a disadvantage if the vehicle has a bulb failure alert system.
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Robert Noel Reddington
Grand Master
Username: bob_uk

Post Number: 887
Registered: 5-2015
Posted on Wednesday, 16 March, 2016 - 10:12 am:   Edit PostDelete PostView Post/Check IP

True LEDs last forever, but my car doesn't blow bulbs. Where LEDs are good is where the bulb is used with engine off such as interior lights due to their low power consumption. And of course for the brilliant idea of fitting a red LED cluster in the reverse light as rear fog lamp. Pun intended . Brilliant.

LEDs that are fitted to modern light cluster as original by the makers appear not to be 100% reliable and I have heard of rear lights blowing and an expensive bill for the new bits. Can bus. Just to make life difficult any lighting faults on can bus and the dash lights up.

Sometimes what appears to be better isn't. The incadesence bulb is very cheap and does the job except that headlights could be better.
The optimum voltage for incadesence bulbs is 6 volt to 24 volts with 14 volts being the sweet spot. Higher voltage bulbs the filament gets finer and delicate. Lower voltage requires fatter filaments which use too much amps for the higher wattages ( say 3 watt and over).

Automotive retro fit LED bulbs are coming down in price. A stop tail is about 7.50 at the moment. And the normal version 0.80p.

Being a retired mechanic I have a box with lots of used light bulbs so for the foreseeable future I have free light bulbs.

I often hear of the fuel savings to be made by proper control of the electrical system.

If the alternator is producing 60 amps at 14.4 volts is 864 watts. Given that the alternator is 80 % efficient. The power need to drive the alternator is about 1000 watts or 1.3 BHP or 0.02 BHP per amp. A stop lamp at 21watts and 14.4 volts consumes 1.45 amps. The stop lamp requires 0.03 BHP.

So as one can see from the maths the savings are so small that it's not worth the bother.

Recently our local trading standards checked out a fuel saving device that plugged into the cigar lighter. It was meant to improve the stability of the electrical system and save up to 15% fuel saving. Inside the device was a circuit that turned on LEDs and nothing else. It's impossible to save fuel like this and 15% I should coco. Even if the alternator was removed entirely from the engine the savings on a ROAD car would be insignificant. Bearing in mind that the alternator doesn't use 1.3 BHP all the time mostly it's running at less than half.

Race stuff is different and no alternator can win a race.

I think my maths may be a bit out but you get the picture.
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David Gore
Moderator
Username: david_gore

Post Number: 1942
Registered: 4-2003
Posted on Wednesday, 16 March, 2016 - 12:15 pm:   Edit PostDelete PostView Post/Check IP

From correspondence on another forum I frequent, failure of vehicle LED light clusters on modern vehicles is a regular complaint, not complete failure in most cases but failure of individual LEDs in the cluster. My partner's car has LED rear light clusters and fortunately has not had any problems most likely due to the fact we live in a temperate climate where condensation is rarely a problem.

Some of the more electronically minded members have found ways to replace some of the failed LEDs but not all. Some with experience in the electronics industry have commented that the standard of manufacture for the clusters sometimes is less than what is required for the application most likely due to cost-cutting by the component supplier to the car manufacturer. Some of the failures have been due to water ingress around the light housings due to faulty sealant application during vehicle assembly; others due to condensation in cold climates from water/snow brought into the car by occupants, water leaks due to faulty window/door seals and water drips when doors are open caused by the lack of a rain water gutter above the door openings [especially relevant to convertibles]. Once this water gets onto the circuit board[s], problems begin to occur.

One step forward and sometimes two steps backward.
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Robert Noel Reddington
Grand Master
Username: bob_uk

Post Number: 888
Registered: 5-2015
Posted on Friday, 18 March, 2016 - 07:41 am:   Edit PostDelete PostView Post/Check IP

Ford C Max rear lamps go wrong and it's not cheap.

The LEDs are ok but it's the circuit board and discreet semiconductors that go wrong. If it was just a live and earth connected to a retro type LED cluster bulb then it would be easy and cheap. But due to designers knowing that there is a Huge mark up on electronics and that they can do clever stuff. They fit unnessary stuff. Also once the car is 5 years old say, who cares if the rear lights fail apart from the owner or victim.

The power consumption of incadesence bulbs is not that large and as said an alternator easily copes with the load. Noting that stop lamps and indicators are not used for long time.

One step forward and sometimes two back.

The R and D should concentrate on head lamps not rear lamps.

If LEDs are so reliable why do we need a warning system that implies that LEDs aren't reliable.

The circuit that gives the warning is the failure point . Ironic.

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