The Stovebolt Site Forums The Shop Area The Electrical Bay Headlight switch?

My headlights here lately have been going on and off as I am on my way to work. The grounds are all good, it seems like the light switch could be the culprit? The reason I am saying this is while rotating the knob back and forth in and out seems to find the correct spot and keep the lights on.. I basically thought just pull the switch all the way out and have lights no matter where the knob is rotated at. What do you think there Bolters?

1. No one on earth can say "all the grounds are good" regarding electrical problems.
2. The headlights go thru the dimmer. Could be the dimmer. Tail lights don't go thru dimmer, see if they are going off and on. They are on a different terminal on light switch however.
3. Could be a loose wire.
4. Could be the light switch.
5. Could be a corroded connection. Does it do it in high beam and low beam?
6. If you think it is the switch, pull the hot wire off of the dimmer switch and tape it's end. Install a jumper from the battery to that dimmer hot terminal.
If no more trouble, it's the switch or switch wiring. Take off jumper when you get to work or lights will stay on.
If you are not good or careful or knowledgeable with electric, or can't do the jumper, buy a new switch.

Year, make and model would be helpful.

Here is a great tutorial on headlight switch repair: headlight switch repair

in my case it was the thermal contact switch within the headlight switch. I burnished the contacts and it worked again, but I lost confidence in it and replaced it with a new one.
don

I have opened up every switch there is. Headlight, ignition, heater, dimmer, wiper, dome, turn signal, fuel sender rheostat......hardest part is getting it open without damaging the tabs/crimps/swages, the phenolic base or losing a little springy dingy or copper thingy.
Whether that's "worth it" or not is up to the individual. I enjoy refurbishing them.

bartamos Don't mind opening that stuff just don't want to burn the truck up,or the shed with it !!

donsz Learned to take out the knob stem, insert WD40 tube clear in spray on the way out to lube it. Of course the thermal is external out in the dust and dirt where you can work it.

OL55 You don't have added load do you ?? Thermal protection is only good for so much,might buff contacts with a business card,they're on the outside.

Looks as if I might have found my light problem? Well not really, but I pulled out the light switch, and the wire for the light terminal seemed as if it was really getting hot a time or too. The plastic insulater was even partially melted? Not sure what this could be?

You mentioned your headlights were going off/on as you drove. The supply wire could be grounding itself out (which definitely would cause the wire/connector to get hot until the thermal protection cut the headlights off). Then the thermal protection would cycle the lights on for a bit/off for a bit as long as you drove. To check for ground, get a handheld electric tester. Set it for the diode checking function. In the first image below, I've done that. Remove the headlights and see what the resistance in the wire leading from the switch to where the headlights should be is. How? Connect one of the tester leads to ground and the other to that supply wire. If everything is ok, the reading should show as a whole number...maybe something like 3.3 or some other whole number (as you see below in the second image). If that wire is connecting ground, you may hear a buzz (if your tester has that function) and even if you hear nothing, you'll see the reading go to all zeros (as in the third image) and some meters may show you some very small number. If you see all zeros or a very small number (like 001 to 007) and you have the tester set for the diode function, your wire is grounding itself. I've added 2 images below showing a really cheap tester I got free at Harbor Fright years ago as image 4 and 5 (4 shows wire not grounded and 5 shows wire grounded). Good luck.

Jon beat me to the punch. Do Jon's check above first. If all is okay then proceed with below.


So the other terminals on the light switch are okay?

The melting insulator is caused by overcurrent.
The current flow pathway is:

Ground (near headlight)
Headlight socket (in)
Headlight bulb filament (low or high beam)
Head light socket (out)
Terminal strip (in) (inner fender)
Terminal strip (out)
Dimmer switch (in) (floorboard or toeboard)
Dimmer switch (out)
Light switch (dash)

As you can see, there are multiple connections (screws or wire connectors) in the current pathway.
If any of the connections are not clean (free of corrosion etc.), they cause a resistance to the current.
The more resistance, the higher the current, the more heat generated.
This is typical of 70+ year old wiring.
It's not that the wires of the wiring is bad, it's the connections.

I clean connections by using a deoxidizer (Deoxit) sold by CAI Laboratories.
There are other contact cleaners. Some are okay. Some are horrible.

DO NOT use penetrating fluid such made by WD-40, Kroil, Blaster etc.
This fluid is made to penetrate rust. It can ruin (or very hard to clean) electrical connections.

Yes...very good point. WD40, PT (Barnum) Blaster or any of those things can ruin any amorphous plastic parts. And it is better to assume there could be some rather than find later you've melted, dissolved or fundamentally ruined the structure of them.

Took off the supply wire that goes to the dimmer switch. Ran a jumper from there straight to the battery like Bartamos said and lights are a shining without any on and off, according to the man, sounds like a switch. Now check it out one of my redneck buddy's has light switch out of a 55 chevy car, it's 12 volt, would that work?

Yes, but after you unplug your headlight switch, do a continuity test on it to confirm it's a bad switch. I'll tell you how if you need explanation. It would be nice to have a multi-meter but not absolutely necessary.

Yes a little education on checking out that there headlight switch would help. I do have a meter here that checks for continuity along with the sounding function also...

You want to check that the "H" (headlight) terminal on the headlight switch has continuity to the Batt terminal on the headlight switch when knob is pulled out. This is done at the bench, No truck wires on the switch. You can test to see what other terminals have continuity to the batt terminals and to each other.
If you find that the "H" has continuity to "Batt", every time you operate knob, then the switch could be OK as far as headlights. It means it may be a bad wire or terminal connection. Maybe a fuse in the circuit and is blown. Previous owners can do some weird wiring quality.

If switch test bad, be sure to do the same test on your buddy's donor switch before install. The switch terminal are marked with embossed letters...H, B, PL, T, S, D, etc. The Headlight terminal can sometimes be called "dimmer".

Normally those switches just need taken apart and light cleaning of copper contacts inside. Maybe a dab of lube on the slider. Check to see springs are not broken. You can stretch them a tiny tiny bit. It takes three hands to get it back together.

EDIT
I say switch could be OK because a continuity test does not load the switch contacts like headlight bulbs do. Weak/corroded/dirty/worn contacts inside the switch can carry a small continuity load but not a service load. So when installing the buddy switch, don't mount it to the dash. Let it hang down with wires connected and test it's operation. It's frame may need to be grounded when switch is hanging. Usually that's just for the dome light.

A new switch is $35....probably $85 by the time you read this.