Can't start, won't start, shorting issue...

[matclarke]

Hello,
This is a interesting one; electrical which is always confusing!

The headlamp switch classically burnt out, partially melting the black wire which is paired to the headlamp's blue wire disappearing off to the "Acc" on the foglight switch.
I struggled home in the dark using main beam only! Allegedly... :-)

I took off the centre console & another black wire, from the foglight switch's "ground", also had to be replaced due melting. This was paired into the clock's black wire...

Even before I installed the new LED based headlamp switch, I noticed that I couldn't turn the starter motor or flash the headlights without an almighty drop in voltage and the console lights dimming, with voltage showing no more than 8v...
Turning off then on again the main battery isolator resets everything to about 12v, bright lights, but no further!
Most things, like the foglight switch are disconnected for trouble shooting, but still no clue...

Perhaps the damage goes further than I can see and is causing a short somewhere?
(Wiggly AMPS! Curse them when they're not going in the correct direction!)

Anyone any suggestions?
Thanks
Mat
Frenchy 3866

[matclarke]

In summary, when I turn the key all looks good, until I either flash the high beam, press the brake pedal, or turn the starter, oh, and the indicators don't work at all, and the horn is intermittent.
Shorting somewhere I'm guessing, but where!? Eek....
Mat

[Chris P]

Hi Matt,

Sorry to rear about your troubles. I'm not expert at eclectics but it sounds as though a hot wire has shorted out other stuff.

What does the fusebox look like?

Can you follow the wire back by carefully cutting away the black insulation tape? I would think you need to inspect the whole run carefully, you could re-tape it all back together once you have located the problem.

There are one way diodes I understand…but i'm afraid I don't know any more about them.

[matclarke]

Hi Chris,
Thanks for the reply...
Yes I think you might be right about a hot wire shorting out other components... Looking deeper needed!
When I get time, yes I will keep going further and cut through the tape....more dashboard coming off me thinks!

Will also look into the one way diodes, I didn't realise about them...

I imagine this problem is directly involved with the headlight switch melting so I've got a good area to concentrate on first!

Coincidently I recently bought a lovely colour A3 electrical layout of the D...highly recommend it.

Thanks Chris,
Mats

[stunned_monkey]

Matt, the voltage will dip when you crank the starter,it draws a lot of current.

The brake and headlight feeds are wholly independent so I'm wondering if your dash voltmeter is the red herring here and what has happened is that your instrument cluster has lost a good ground because of the mesed up headlight switch, expecially if tha failure was caused by something in the switch grounding via the bracket. Everything you have described could be caused by a dodgy connection on the side of the stereo bracket. Make sure that is tight, clean and as a quick test, run another wire from it to a good ground (the gearstick will do for a quick test).