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Bob uk
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Posted From: 94.197.122.73
Posted on Friday, 29 August, 2014 - 11:07 am:   Edit PostDelete PostView Post/Check IP

I have just been reading electrical problems on SZ and later and oh dear the amount is quite staggering.

A safety tip often it is necessary to go in hot with live circuits some of which are not fused so disconnect the battery earth and link back up with a piece of thin wire or a say 20 amp circuit breaker.Depends what you testing. 20 amps will allow 240 watts.

I always get the circuit diagram first study locate the bits I am interested in, in the diagram and on the car. Without this I have wasted time removing trim from the wrong place and ended up with a big mess of wiring and relays. Mistaking a cruise control unit for a abs unit. Also try to figure out the colour code rational such as Lucas use blue to the dip switch and blue red for dip and blue white for main beam and red only for side to correspond to the dip. So any red wires around the back of the car are tear lights. This halves the Work.

Then I draw out a circuit with the colours and plug numbers. Because it's my car I make a decent job of the drawing and file in the history.

Then I look for bad connections. Visual for verde green traces then wiggle the cable crimp. Then probe either side for continuity.for instance on SY foot wells the door wiring falls apart any window problems look here first. For New plugs and sockets vehicle wiring products VWP.

Wires very rarely break in the run. If a wire is green under the insulation then it is u/s.

Most modern wiring is crimped because soldered joints are inferior and taken longer to make. Some modern wiring has nylon filaments woven into the copper these won't solder and should be crimp or temporary choc block.

All RR switches feel positive and definitely tell you that the switch has worked sort of feel. If they don't then that might be the problem.

Relays are easy to test off the car using the circuit diagram. If they work they work and say working. Some have a replaceable fuse attached, Ford liked these. If it's as Ferrari fit Bosch or Hella not marelli.

ECUs in modern cars are quite reliable and robust. Onboard diagnostic probe costs about 30 in the UK and will save an immense amount of time and in some cases the fault will be impossible without it.

Once the dodgy bit is unidentified the code only knows that the data from the what ever is wrong meaning that it has checked the whole circuit not the whatever. So double check the whole of that bits wiring especially engine looms.

Handy stuff digital multimeter with buzzer. Good lighting tiny gas soldering iron . Sharp sewing needles for pushing in insulation to get a connection. Maplins sell test leads with tiny sprung grabs. Aerosol electrical contact flush spray. Not WD40. To recover corroded copper vinegar then clean use petroleum jelly on assembly. For furry batteries hot water plain nothing added.

ECUs do go wrong and can only be tested by specialist equipment. When I have exhausted the wiring. I know of a place that will test and repair or exchange for good one they have loads of ECUs my jeep was 65. Or 180 New.

Any lighting problems check earths with circuit on by measuring from live to to known good earth and suspect earth, the voltages must be the same 1/2 volt points to dodgy earth -- somewhere.

To check engine earth fit amp meter with 5amp fuse in series with the engine and the chassis or battery earth terminal and crank engine if the ammeter shows a reading then the earth strap is bad. If the fuse blows then the strap is even worse.

(Message approved by david_gore)

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