rear light fault, earth?

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andy198712
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rear light fault, earth?

Post by andy198712 » Mon Jun 12, 2017 10:11 pm

Hi,

i'm getting a 2002 1.4 polo ready for MOT

when i press the brake the warning light on the dash for the rear fog glows....

i noticed someone has added an extra earth cable from the orange bulb (literally wedged down the side of it) to the brown wire an inch after the plug.... which sent off alarm bells. (passenger side)

is this a common issue?

plan of action is unplug the light and see if it does it, then try the other side, test again.
then remove bulbs and test both sides like that.

any tips or people had this before?

i followed the cable loom back 12 inches where there is a few plugs and they look a tad green in places! earth looked okay though.

i haven't fully tested all the bulbs yet which will be one to try, but can't see it causing this issue surely?


Cheers
Andy

andy198712
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Re: rear light fault, earth?

Post by andy198712 » Tue Jul 18, 2017 7:21 am

so now when i go to indicate left, the light on the dash goes fast (blown bulb) but none of the 3 indicators on the left hand side work? don't work for hazards either.... thoughts?

Cheers
Andy

RUM4MO
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Re: rear light fault, earth?

Post by RUM4MO » Tue Jul 18, 2017 6:17 pm

The first thing that I would do would be to make sure that the metalwork on the part that the bulbs are located is still usable - ie no rusting. After that you should run a length of wire down from the front of the car, from a suitable earth point, to the earth point of that cluster and solder it on if possible, then see if everything works okay, if so try to find a suitable body earth point near the rear of the car and run that wire now from the cluster to that earth point.

Edit:- maybe after everything is back working okay, you could tidy things up by identifying the incoming earth wire to that cluster, unwrap a length of the cable, remove some of that wire's insulation, and wrap round then solder the new earth wire to that wire, then wrap the repair with insulating tape and then rewrap the cable with cable harness wrapping tape.

Another Edit:- you will also need to use a voltmeter to check what is happening as I've just remembered that you said the left side does now not work at all, I'd think that you have caused a short circuit to earth at that rear cluster, ie indicator 12 volts to earth short?

andy198712
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Location: Cornwall

Re: rear light fault, earth?

Post by andy198712 » Tue Jul 18, 2017 7:09 pm

i'll get probing tomorrow with them on and see if they are getting a 12v intermittently (flash) then i can narrow it down to earth... odd how its the whole left side? the indicator light on the dash still works but just flashes fast, as if a bulb is out.

thanks for the ideas, I'm pretty sure that rear cluster has a body earth near it... which looks clean but will inspect!

Thanks :)

andy198712
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Posts: 12
Joined: Sun Feb 12, 2017 3:47 pm
Drives: '72 Beetle
Location: Cornwall

Re: rear light fault, earth?

Post by andy198712 » Tue Jul 18, 2017 7:09 pm

i'll get probing tomorrow with them on and see if they are getting a 12v intermittently (flash) then i can narrow it down to earth... odd how its the whole left side? the indicator light on the dash still works but just flashes fast, as if a bulb is out.

thanks for the ideas, I'm pretty sure that rear cluster has a body earth near it... which looks clean but will inspect!

Thanks :)

RUM4MO
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Posts: 2142
Joined: Sat Dec 30, 2006 9:12 pm
Drives: B8 S4 & 6R/6C1 1.2TSI 110
Location: Mid Lothian

Re: rear light fault, earth?

Post by RUM4MO » Tue Jul 18, 2017 7:15 pm

One point, and I discovered this obvious point many years ago, beware of high resistance in the supply wires or earths! I found this out on an old Fiesta, I measured the 12 volts supply to the rear wiper with the wiper unplugged, it read 12 volts so okay - no, the wire was almost completely cut through and when loaded with the wiper motor, the voltage at that motor was almost nothing! Just something to bear in mind when working with car supplies.

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