Need electrical help - lighting wiring gone haywire

zzwhm · 12-30-2007, 05:38 PM

The headlight switch on my 87 911 melted and I thought the problem would be an easy fix by replacing the headlight or turn signal switch. So today I replaced the headlight switch, disconnected the turn signal switch and turned the car power on (via kill switch) - here's what happens

- the horn goes on with the headlight switch in the off position

- the brights come on with the headlight switch pulled to parking lights

- the headlights come on with the headlight switch fully pulled and the rheostat controls them

- left turn indicator on the speedo lights up, though I'm not certain this occured every time I tested

- the headlight switch quickly gets hot and if left on would quickly burn, again

All of this occurs with the turn signal switch disconnected. I tested the turn signal switch off the car and it seems fine, it's fairly new. I put in back on and it had no effect.

Pulling the horn relay causes the horn to stop but the headlight switch is still overloaded.

Anyone have suggestions for how to isolate the source of the problem?

Thanks.
Bill

billybek · billybek's Garage

Wow, I bet your head hurt when all that was going on!!!
You might have a few wires that have melted together as well.
See how pulling fuses for the different components changes what is going on. Mind you you might have a fire while you are trying to isolate it.
Do you have a good wiring diagram for your car?

saint914 · 12-31-2007, 04:24 AM

HI, I'll take a shot at that one(a shot in the dark for a bad pun)
I think the firewall connections for the headlamp switch and the dipper switch may be in the wrong sockets. These are the round connectors in front of the switches pass through the fire wall.
Hope this helps.
Geoff.

Mo_Gearhead · 12-31-2007, 05:34 AM

QUOTE: "the horn goes on with the headlight switch in the off position

- the headlight switch quickly gets hot and if left on would quickly burn, again

-All of this occurs with the turn signal switch disconnected."
__________________

I agree with Billy K.

It sounds like you have overheated some wires in a bundled harness and some have 'fused' together. You need to get up under the dash area and trace out the wires, look for a melted area. May have to strip off some of the factory tape wrap that bundles them.

Potentially a car fire in the making!

Get a wiring schematic and start tracing back-wards. Not a fun job. Sorry.

zzwhm · 12-31-2007, 06:43 AM

Quote:

Originally Posted by Mo_Gearhead

You need to get up under the dash area and trace out the wires, look for a melted area. Get a wiring schematic and start tracing back-wards. Not a fun job. Sorry.

That's the plan for today. With the steering wheel off and after pulling the seat at least I won't be quite so badly contorted as yesterday.

Since this all started I've driven the car a couple of hours with the headlight switch removed (its a track car) and nothing bad happened, so the wiring to/from the switch is where I'll start.

None of the fuses blow so the problem seems to be between the fuse box and under-dash wiring.

Bill