Two Headlight switches burn up in two years?

[mfiazzo]

Hi All,

As always, thank you for reading my question and helping.

Something going wrong with my headlight switch.

Back story:

Two years ago, I was driving at night with the headlights on. I smelled the unmistakable smell of burning wires. I then saw smoke pouring out of the dash where the headlight switch is. I quickly turned the headlights off and pulled the switch from in back of the dash. Sure enough, the switch was burned, I saw melted plastic on the switch. The switch also looked to be original to the car.

I replaced the switch and all seemed to be OK. Then last night, I was driving the car at night with the headlights on. I stopped by the store turned off the engine and inadvertently left the headlights on. When I came out of the store, same thing happened smoke pouring out of the headlight switch. When I started the car and turned the headlights back on all seemed to be OK.

I pulled the switch this morning and the switch is visibly melted in a couple of spots. The switch still works however. It smells really bad though.

So my question is.....

What gives, just two bad switches? I did notice last night, a couple of the wires are extremely hot. Is something else going wrong. A short in one of the headlamp perhaps?

[MrScott]

What year is your car?

The dashboard lights, ventilation lights (and I think ashtray light) are unfused and powered off the headlight switch but they're thin wires so they'd smoke before the switch. You should fuse them regardless (single in-line fuse, easy job, search for instructions) but I don't think that's your problem.

You say you "left the headlights on." With the key out and the headlight switch "on" only the parking lights should illuminate. Is that what you mean? And the smoke started with just the parking lights on? If so the problem seems to be in the parking lights. Those are fused from the factory. Do you have the right fuses installed? As a first step I'd go through every fuse in the fuse box and verify it's the correct rating.

Then follow the hot wires. Are any wires melted or discolored? Look under the dash, from the trunk look behind the gauges. Others should confirm but I think in every circuit powered off that switch the wires will start to smoke before the switch - there'd be evidence of that somewhere.

[DRACO A5OG]

Did you place relays second time around? If not consider doing so once you replace the charred lines. +1 make certain you have correct fuse

[jlex]

^^^^ This.
Here you go for headlight relay fix: 1988 Porsche 911 Carrera Coupe - Lights and Lenses - Page 10

[MrScott]

The relay kit is a good upgrade but to go from shorting higher current to shorting lower current isn't a fix. If it smoked with only the parking lights on the relay kit won't help at all.

[Synchro Joe]

Have you traced out the ashtray light wiring by chance? If any lights are on, the silly little ashtray light is energized and if it's loose and flaying about, it can short out the wiring to and from the switch. One I experienced did not ruin the switch entirely, but did take out some other wiring in the bundle. Any melting of the switch terminals, etc. ?

[mfiazzo]

Hi MrScott,

The car is a 1978 911SC. I left the key in the ignition with the engine turned off. I inavertantly left all of the lights on, in other words the headlights were on, since I was driving at night. The headlight switch was pulled all of the way out.

I did not upgrade to the relays nor did I add any fuses when I replaced the OEM switch. It is definately the switch that is burned as there are melted marks on it. It still works however.

I traced out the ashtray wiring, the wiring seems to be OK. The bulb was burned out and where the connector attached to the bulb socket was missing the little rubber bootie that covers the connector. I went ahead and pulled the bulb and taped up the entire socket and connector with electrical tape. I do not use the ashtray and keep it closed. So I do not need a light.

[canamfan]

Are you running "stock" bulbs in everything, including parking lights? Are there "any" upgrades to the lighting system (LED's, higher output bulbs anywhere in system etc.)? Is/are there any equipment (ie. stereo, alarm, extra lights) being wired directly (or near) the headlight switch?

[mfiazzo]

no, all of the lights are stock. No upgrades to the lighting system. No alarm system on the car, the stereo is wired with a fuse in it, not anywhere near the headlight switch

[boyt911sc]

Originally Posted by mfiazzo

no, all of the lights are stock. No upgrades to the lighting system. No alarm system on the car, the stereo is wired with a fuse in it, not anywhere near the headlight switch

Mike,

About 20 years ago, my turn signal over heated and melted. Replaced the switch and installed a 'Sucro' headlight relay unit. Headlights upgraded to higher wattage and has been trouble-free since then (knock on wood). Consider installing a headlight relay to prolong the life of your switches and lamps. We both have '78 SC cars.

Tony

[theiceman]

put the relays in and call it a day ... goes from amps going through the switch to milliamps.

[wolds]

In addition to relays you NEED to make sure all coonections are oxidation free and mechanically tight. This includes your GROUND wires. I have preached this before and cannot stress how important this is . You can put all the relays you want in the system, but if you have suspect connections you won't solve your problem.

[MrScott]

Alright since it's likely headlights the relays will help. I'm still worried the fuses aren't doing their job. Check your light fuses for correct ratings.

+1 on grounds. You can do this when you install the relay kit. I recently cleaned up the ground by the battery and (if my el-cheapo cigarette lighter voltmeter is accurate) voltage increased by around .2V.

[theiceman]

Originally Posted by MrScott

Alright since it's likely headlights the relays will help. I'm still worried the fuses aren't doing their job. Check your light fuses for correct ratings.

+1 on grounds. You can do this when you install the relay kit. I recently cleaned up the ground by the battery and (if my el-cheapo cigarette lighter voltmeter is accurate) voltage increased by around .2V.

they arent , the current required to burn the switch is far less than the rated current going through the fuse. ie the switch acted like the fuse.

once you put the relays in if it wasn't the contact in the switch causing it you will start blowing fuses, NOW you can troubleshoot. burning the switch doesnt always mean dead short , it simply means too much heat at that connection and as pointed out a flakey contact can cause this . We see this over and over with the fuel pump connection at the fusebox on SC fuel pumps.

[mfiazzo]

Thank you all for the help. It is much appreciated. I just ordered the relay kit from our host.

One additional question. In some of the other headlight issue posts it was recommended to install a 3 Amp inline fuse to the ashtray light. Should I still do this along with the relays?

Here is that post:

Headlight switch let the smoke out!