Headlight switch is burning , ah!

[Kartrdad]

Scaring situation. was getting my 1986 930 set up for a little run and all of a sudden I’m getting a plume of wine smoke from under the dash , followed by a mad scramble to disconnect the battery



So looking for some assist as to the cause ,
Is the switch the culprit ? Or is there a wiring issue to search out?

Thanks in advance for any input appreciated.

[slotmeister]

Hi - I'm hopeless with electricity, but I discovered (when my headlight switch got hot) via this forum that it's a known issue, with the relatively simple fix of installing a relay. Or, in my case, having one installed. Cost just a handful of bucks for complete peace of mind. You should find lots of info with a search on this forum.

[JSV798]

Looks like that switch is fried. You need to install relays so that the switch just takes a small current and not the full load to the lights. Did you have the lights on? Not sure why it would burn if the lights are not on. The switch can be taken apart by drilling out the rivets and replacing with small bolts. You might as well give it a go as you have nothing to lose with that switch and you might be able to repair it as a new one is over $500.

[cabmandone]

Have you checked fuses to make sure they're all of the proper size? Also as JSV798 said, get a headlight relay kit. The kit is easy to install and the relay carries the current for the lights where the switch just operates the low current coil of the relay.

[Driven97]

Since a specific product isn't mentioned above, I used the JWest brand headlight relay kit available at our host. As mentioned above, the OEM design has the switch carry the entire circuit current and that type of failure is known to happen.

A new switch is megabucks, I'm surprised an aftermarket replacement isn't available.

[targa80]

Looking at the pictures i see the heat damage to the switch but are any of the wires damaged? If you do have a damaged wire then check the schematics to find the branch that is causing the over current issue. I have no knowledge of how the 86 model is wired for headlights. I do know that on the SC models the switch can fry if you upgrade the headlights and not add a relay to handle the extra current load of the higher wattage headlights.

[bdisco]

http://www.pelicanparts.com/cgi-bin/smart/more_info.cgi?pn=JWST-911-HLPR&KeepHeader=Y

I have this kit sitting under my work bench waiting for warmer weather to be installed.

You might want to add this to your shopping list.

[BlueWing]

Also add an inline fuse to the dash lights circuit. That is also a potential spot for Porsches brand of Lucas Smoke.

I did a quick search and didn't see it right away but IIRC Terminal 58 on the switch with 2 black and blue wires. Search out the thread with detailed pictures and instructions. A sub $10.00 fix for a point of missed protection.

Terry

[porschenut]

Your thread title says "headlight switch", but you are holding a picture of the LIGHT SWITCH, which is a 2-position switch. You need to tell us which position you put the switch in when the smoke occurred. If it was not in the 2nd position (fully out, for headlights), then having a headlight relay would not have prevented this from happening.

Whatever the cause of the terminal burning out, it was in the switch itself, not in the wiring, or else you would have melted wire insulation and/or melted copper. And as a reminder to others, all of the exterior lighting circuits are fused, including the headlights. Fuses prevent over-current situations. That is their sole purpose.

Was there a wire connected to the location where the burn evidence is shown in your picture? And if so, where is that wire now and what does it look like?

[JSV798]

The light switch is supplied with power on line 30 (direct from battery for headlight flash)) and line X (from ignition switch) for parking/low beam, neither of which appear to be fused, according to Haynes, pages 298/9. So light switch is always hot on red wire and hot on the thick red/white wires when ignition is on. The fuses are downstream of the light switch, where the relays would be added. I have fitted relays but so far have not introduced a fuse upstream from the light switch. My car is a '78 SC so might be different.
The fried part looks close to the red/white wire which I think would become hot when the ignition is turned on. Is this what happened?

[porschenut]

I don't have the wiring diagrams available at the moment, but at least on the 84-89 Carreras both the low beams and high beams of the headlights are fused at the fuse panel. 4 fuses in all. Power is supplied to the light switch via the ignition switch. When the switch is pulled, power is then sent to the fuse box, where the circuit continues through the fuses to the running lights, or running lights and headlights, depending on the switch position. It isn't necessary to place the fuse "before" the light switch, as current flows everywhere in a circuit, and cannot flow anywhere in that circuit if the circuit is broken at any point between the positive and negative terminals of the battery. If any electron can't move, none of them will move.

[70SC]

Dash lite dimmer control. If the dimmer control gets turned to hard it can upset the windings as you can see. I just had to do one in a clients car last month. Glad it didn't burn.

[Walt Fricke]

I don't see how you can repair this switch. Driving home from skiing one winter the headlights went out, and no jiggling could fix. Luckily, I had fog lights.

I took the switch apart. Very well made design. But a silver looking (might actually be silver?) internal contact on a ceramic core which holds various contacts and connections had burned. How are you gong to repair something which doesn't really come with separate parts?

I got a junk yard replacement, and installed relays for highs and lows. Relays also help keep the stalk lever switch happy for much longer.

Making a switch like this would be very expensive, though perhaps some different design would not be.

[Duc Hunter]

I had one do something similar. It was not turned on and not disturbed. The switch dimmer function shorted some how. What did I learn? Relays!

I did the Classic Retrofit Fuse blocks on al my cars. Kills 2 birds with one stone and easy to do realitively speaking. Blade fuses (round fuses and their 25yrs old or more fuse blocks are another source or electrical issues and fires) and their fuse blocks have headlight relays on board.