Technical I keep burning up GM Headlight Switches

If you’re measuring through the wire that connects to the lights, you’ll have a few ohms to ground, due to the resistance of the filaments. I/e one side of the bulb gets power, other side is to ground. Now the more bulbs in parallel, the lower the resistance. If two 2 ohm bulbs in parallel, then you’ll have 1 ohm to ground.
Take the bulbs out of the sockets and test again.

 

Time to step back and take a break. We/I can’t help much with out being there. Just take away with this. A headlamp lamp switch is a multi function switch and 12 volt distribution. Break them down by studying 60’s GM wiring diagrams. Good luck

 

I agree, either remove all the dash lights, including bulbs for ignition switch and cigarette lighter/ash tray, radio too. Or you can remove the sockets for those bulbs. Then check for low resistance from feed wire to ground. You can also use a trouble light from feed wire to a 12v source. If light lights up you still have a short.

 

I was thinking there wouldn’t be any connection at all to ground. I will start chasing bulbs…tomorrow.
Thanks

 

The ohm test on bulbs will show continuity to ground because it’s path IS to ground through the filament. The filament only turns into a light when it has voltage/amps on one side and ground on the other. Like others have said, fuses are your friends (or at least circuit breakers). The green/grey wire is positive supply to the gauge lights and the white is ground according to the picture you posted. Check to make sure switch is the same with your meter.

If everything is the same you can wire in a automatic circuit breaker in the problem wire, hook everything back up and un plug each wire in the circuit one by one until the circuit breaker doesn’t trip off anymore.

Also physically check that the wires aren’t touching anything, trace the wires to make sure they go to the right spot.

 

Was the large silver terminal connection on the old switch mounted to ground ? I dont see a wire on it . Is yourdash where the switch mounts wood ? The switch ground terminal, just next to the burn is what Im talking about . If your dash is wood that switch needs to be ground.

 

You need to use a meter to measure amp draw on the dash light wire, ***uming you have a 20 amp fuse on the wire feeding the tail/dash light circuit to the switch it should blow if you have a short in the circuit before burning up the rheostat in the switch.
With the state of replacement parts today I would suspect a defective switch first especially if it was a Standard Ignition T series product.

 

The ground is only used to operate the dome light function of the headlight switch.

 

One problem with measuring DC current, good meters are fuses internally with a 10 amp limit. An inductive DC meter is high dollar. An accurate ammeter could be wired in place , but may become ***bersome.

 

You are not looking at microvolt accuracy here under over 10 amps(+/-2) will tell the tale.
https://www.amazon.com/AstroAI-Mult...=dc+current+clamp+meter&qid=1662238283&sr=8-6

 

I agree with Mr.48chev. Following those circuits 1st.

 

Yes suppose to but look at the bottom left of his switch. Thats appears to be where the rehostat ( spell) grounds to . If so AND theres no grounding anywhere else , the switch is looking for a ground and grounding through the rehostat . I think

 

The rheostat does not need a ground to function the ground is only for the function of twisting the knob all the way to the left and turning the dome light on.

 

It sounds like that ground pin is only for a dome light, which I do not have. My plan is to either find a circuit breaker (which I didn't even know they made for DC) OR just swap one wire back onto that headlight switch pin at a time until it starts burning again- it's not like I'm going to run this one!

Supposing I figure this out- what size fuse should I run between this switch and the gauge lights?

Also, the wires aren't touching anything they shouldn't be. I'm guessing the problem is in one of the bulbs or sockets.

 

I’m on my phone now and not smart enough to paste a YouTube video by American Wire. They have a great animated video of each wire and how current enters and exits each terminal. When I get to a computer I’ll copy and paste it.

 

Technically, the fuse is there to protect the wire, so a fuse correct for the smallest wire in that circuit would be good, what fuse goes with what wire size you'll have to look up.
Anything between that size and slightly larger than the gauge lights actual current consumption will work fine.

 

I will grab an in-line fuse for 20 A and try a 10 amp fuse first.

This morning I just started connected wire by wire until I found out which one made the switch smoke. It’s the light for the speedometer, and the speedometer is not accurate anyway. For now I’m just going to leave it out of the mix. Hooking everything up now. Then I ran into another issue…what is this hokey thing in my fuse panel?

it has a br*** connection in it that’s just floating around, and says off on on the side of it. There isn’t enough slack in the wires for me to see what the hell they are. In a sea of red wires it just kind of moves, but one’s red and one’s purple. The hokey part is why the hell someone drilled through the side of the amount for the panel and into this item.

 

^^^^^^^^^^^^^That looks like a broken toggle switch, not drilled into??

 

If you look at the hole drilled in the silver mounting frame, it lines up with the hole in this “thing.”

 

That is a broken toggle switch. I have one on my car mounted on the fuse box also. It kills the ignition when off. If your car has no power to the ignition that's why.

 

Good morning I see you found something of concern but as I promised last night here's the animated video of head lamp switch wire terminal connections and flow for each operation.

 

Glad to hear that you found the short. That's a "HAS"!! 1/2 ***ed switch.

 

I think you’re right- a broken toggle- I DID have a problem with it nit running recently but didn’t find any toggle pieces on the floor so it’s probably been like that for awhile.

Thanks everyone.

 

I found what will be a spare headlight switch today- or a sacrificial one- and Echlin from NAPA this time, but an NOS switch from the late 60s is en route...

1. About the wiring- my current setup has both of the 12v terminals UNfused. Looks like in that video, the one that's supposed to be fused runs the dash lights. IF that one had been fused, would this short circuit have started burning? Would installing an inline fuse protect all of the ***ociated circuits- (Park, Tail and Dash lights)? What size fuse SHOULD that be? My original plan was to just run an inline fuse between the dash lights and the ***ociated terminal, but I could use that inline fuse on the 12v fused feed, instead.

2. If the answer is that it does not protect those downstream circuits (and would not have prevented these switches from burning up), do all of the terminals coming out need to be fused?

 

Usually use a 15 amp fuse on the tail/dash light circuit and a 30 amp breaker on the headlight circuit.

Others will probably have different ideas.

 

^^^^^ add a 5 to 7 1/2 amp fuse after light switch/before the dash lights. This way if you have a short on that circuit at least you’ll still have tail/stop lights. Make sense?

 

I use this wiring with halogen lights with Forward running off when Headlights on

 

I think mine are like that- no front parking lights with headlights on.

So- my plan is to fuse that 12v feed that should be fused for park, dash, tail lights (15 amp?) and then fuse just the dash with 5 amp fuse.

Or should I do a 15 amp automatic breaker to the 12 v so that if there’s another dash light issue the fuse will blow and if breaker trips it will reset itself? Seems too advanced for me!

 

Ive seen bulbs short circuit when the element dies. That’s always fun to find.

 

Plan 1 seems best don’t you agree? Simple traditional protection.