Electrical Headlight Fault

[rixy 0]

hi, i recently had a new alarm fitted on ma raddo, and when it came bak the headlights didnt work anymore! I pulled out the switch and noticed the brown wire going from the switch to the fuse box,had melted through and was stuck to every other wire in the loom! I removed theswitch to fuse box loom, and cut the wire out, and then re-soldered a new piece in!

 

However, it appears this is not the main problem, with the fuse box tipped down, the headlights and dipped beam work fine, however as soon as you tilt it back to its proper position, all the lights fail! I was thinking, if the wire was melted to the fuse box, maybe its melted or has a bad connection from the f/b to the headlights!

 

If this is so, can anyone tell me which loom it may be, or what one to look for, so i can try to rectify the problem! If this is not the case, and anyone knows of anything else to try, id be more than happy, cheers

[Supercharged 2]

rixy, not got time to post the full info now (gtg out) but me and RW1 have had the same thing happen as a result of a faulty switch...

 

I will give you more info tomorrow if RW1 hasn't seen this - he may be able to supply you with a new cable for the loom but you must test the switch with a meter before trying it again...

[RW1 0]

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Oh dear not another one. Sorree to hear this. It doesn’t help that the later headlight switches only last about 750 to 1,000 hours (about 3 to 4 years driving) in use before failing due to internal heat generated by the small the two small 1.2 watt lamps. I’m surprised this whole affair hasn’t been sorted as this has been occurring since the mid 1990’s and until recently I didn’t understand the mechanism that caused the failure and why the earth wire fries so badly. It borders on the line of a recall as in the extreme this could get ugly and cause a fire inside the dash. Read on……..

 

Right first things first. The whole set of wires in this loom are not protected by fuses. So be careful with what you are doing with the battery still connected.

 

**** I would highly recommend that you disconnect the battery as soon as you have read this post. And leave it that way until the loom is repaired or replaced. ******

 

The earth wire you mention will have been shot from END TO END as you have found and is now possibly other loom wires carrying un-fused 12 volts are bare copper metal wires on bodywork inside the dash where you cannot get at it quickly!! There are no fuses to protect this part of the loom and it could badly short itself. (Hence why the lights work and don’t work when the fuse/relay panel is moved.) Nothing to do with the switch now as the damage has been done along the whole length of the loom. This can now lead to further shorting and the headlight switch, which could have started it, will continue to contribute to more damage by heating up the brown earth wire.

 

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Understand the circuit in the loom first. The THIN earth wire (brown) is there in the loom only to provide an earth return for the little switch lamp that lights the lamp symbol on the rocking switch cover when the ignition is switched on. The sidelights, headlights and the sidelights ON warning illuminated ring on the rocking cover do not use this earth wire. That's why the brown wire is only a thin one.

 

This loom carries ALL the lighting 12 volts power wires for the lights except for the foglights which operate on a different loom using a fuse box relay. The two thick wires in the loom red and black/yellow carry the 12 volts from the battery and ignition respectively.

 

Unfortunately, the switch can short out the battery volts (sidelights) or ignition volts (headlights) due to being partly broken but still working or if new replacement - faulty in manufacture. Faulty in manufacture is that one of the mini lamp's soldering points inside the switch is right next to the earth contact and can be bridged by poor soldering and therefore 12 volts is shorted directly to earth! This applies to all headlight switches, old style or new. There are electrical checks later on to spot this before fitting a switch.

 

When one of the two plastic arm levers breaks inside the switch, which operates the sliding switch contacts plate, then this puts the slide plate into a skewed sliding position, which allows the switch to make a short possible between 12 volts and earth. The two 12 volts supply wires are heavy duty (to supply the lights) and so can carry a fair few amps but the earth wire that now becomes the shorted return can carry very little. So the earth wire rapidly heats up like a giant fuse and the insulation melts as can be seen – end to end. It only takes about 3 to 4 seconds to do the damage shown!!

 

SO PUTTING SCREW DRIVER IN TO OPERATE THE SWITCH OR FORCING THE SWITCH COVER TO AN EXTREME “ON” POSITION IN A PARTLY BROKEN STATE (ie. one of the rocker cover internal levers has broken) CAN CAUSE AN UNFUSED SHORT TO EARTH!!!!

 

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The loom is about 3 feet long and goes from the dash facia headlight switch location over a bodywork bare METAL frame and then directly down to the middle blue connector in the middle of the fuse/relay panel top row of connectors on the backside. The loom is clipped in a couple of places along the way. Easy to get out once the underdash panels/shelves are out and the fuse/relay panel is out and hanging loose.

 

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The main reason for disconnecting the battery is that in melting the earth wire in the loom, it may have melted the other loom wires (12 volts) and if these are now bare at the bare METAL frame, a very big unprotected short can occur powered by the battery or ignition circuits.

 

It is not advisable to drive the car any longer until the loom is FULLY REPAIRED & INSPECTED or REPLACED. (For the later dash style the loom is 535 971 055B, but for late 1994/5 cars it will need a further minor mod to the dim-dip connection (yellow wire) to bring it upto the 535 971 055G latest standard [which can't be ordered at VW], early dashes it is 535 971 055).

 

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Checking a replacement headlight switch before fitting:-

 

With a meter on resistance setting, place one of the meter probes on the pin marked 31. Now in all three switch positions (off – sidelights – headlight), go round ALL the other pins. All should be open circuit with one exception relative to pin 31. If the switch has the original filament small bulbs fitted then pin 31 to pin X will show 16 ohms +/-3 ohms (unless it’s blown). If LEDs have been fitted, then on the ordinary Ohm settings on the meter (not diode test), it should be open circuit. If no direct short is detected in the any of the above tests, the headlight switch is safe to fit to the headlight loom in the dash.

 

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A further protection precaution:-

 

A further precaution during loom repair is to fit a 3 amp blade fuse like the rest of the Corrado’s fuses in an in-line fuse holder in the earth wire (see photo) to protect the earth wire in the event of the switch internally shorting and the messy consequences. The actual current for the small internal switch bulb powered by the ignition is 80mA, so any type (such as glass cartridge filament & holder) of fuse about 0.5 to 1.0 amp is adequate to stop the earth wire being fried. If it blows, the little ignition power lamp symbol on the switch will stop working but the sidelights & headlights will not. If the fuse blows, do not refit a fuse until the switch has been checked out as there has been a short inside the switch, either permanently or momentarily which needs to be corrected.

 

This mod should be done, even if the present switch is working OK due to the unreliability of the headlight switches.

 

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Rixy,

From above, the dicky lights are not using the brown earth wire. So even if it’s a bad repair, the lights will still work but the little ignition driven bulb symbol on the switch cover won’t be working.

 

Either the blue plug is not fully home & locked in it’s fuse/relay panel socket or another loom wire is damaged. You need to inspect the loom off the car visually and line out each wire including some bending motion to represent the fuse/relay panel being tilted.

 

There are no relays on the panel associated with the headlights themselves. It’s all directly wired.

 

PM me about a repair to the loom if required.

 

 

 

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[Adil 0]

I had few problems with some electrical items after accessing the fuse box. It ended up being the relays being loose in fuse box. Might be worth giving the relays a small wiggle to see if anything changes?

[rixy 0]

right o, will check the loom tomorrow, and see what happens, what the prob may be??? cheers, will let ya know how i get on

[Craig 0]

off subject here, being nosey rixy how did you get insured on your storm as im with norwich union, just turned 20 and got a g60 and they only just insured me as apparently you've got to be over 25 for these cars! they let me off as i got a quote from some indian so they had to insure me as i had the quote ref. got 2yrs no claims and pay £1600 fully comp.

 

soz to be nosey just wandering how you got insured as no one else would even let me finish as soon as i said g60, age 19.

[Supercharged 2]

RW1, Excellent post.. 8)

 

I'll move this to Interior.. (I think... :? )

[RW1 0]

Pity there isn't a forum called electrical ( & maybe also a diagnostics one)???

 

 

off subject here,

 

Yeah! Use PM!.

 

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[Craig 0]

will do next time :thumb right:

[dazzyvr6 0]

i think rw1's post should be put into the knowledge base?

[RW1 0]

OK by me. It will be part of a bigger light circuit PDF if I can get round to finishing the file.

 

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