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

1947 3100 with 235 engine and 6 volt system. My park lights work but not my headlights. How can I check to see if the dash switch is faulty? Thanks, ray durham
UPDATE 03/28/26
Headlight problem has been resolved. I'm ashamed to say the headlight wire that plugs in at the dimmer switch was disconnected. Thanks to everyone for all your help.
I'm about to make a post about my turn signals and horn.

First, make sure all your grounds are perfect and clean. That's a 00 gauge ground cable and 00 gauge starter cable. Body to frame ground, etc. Take them off and wire brush all the terminals, connections, etc.

Make sure all headlights are grounded, too.

You can temporarily use jumper cables to ground everything and see if the headlight come on. If they do, go back and fix all your grounds.

I'd also hot wire the headlights to make sure that the lamps work. If they do, just work your way back through the circuit to find the problem.

What Otto said. Also, you can pull the headlight switch and test it. They are prone to fail. I needed to replace mine, as well as the dimmer switch on the floor. Any place in the headlight circuit that has a bad connection can be the issue. Start with the easy stuff, like at the terminal blocks on the inner fenders. You could jumper between the park light terminal there over to the headlight terminals to check the bulbs, but like Otto said, if the grounds (one screwed to each inner fender) aren't making good connection, the headlights won't work.

I have a '46 and I believe my head light wiring goes from my switch to the high beam switch on the floor and then to the head lights. Maybe step on the button to see if either high/low work? After testing the grounds, maybe you can move the head light wire on the switch to the tail light lug and see if you get head lights? Maybe you don't even need to move the wire, just test the lug with a multi-meter when you pull it on. I think that can tell you if the switch is working? Disclosure: I'm not a wiring expert by a long shot.

I actually have to wiggle my switch a little to get the head lights on, so I might be replacing my switch soon.

Any power that goes to the headlights goes through the dimmer switch.
A good place to find corrosion and bad connections.
Fred

Somewhere there are instructions I wrote a couple of years ago on how to disassemble, clean and make your headlight switch work like new again. Please search for them. They may have actually become a tech tip in this section.

Well, taking a moment to look I see it never became a Tech Tip. However it is still present and you can see it here:

https://tinyurl.com/y6f3lbgs

Hope it helps.

Very good post Jon with lots of pictures - just how I like them!

I recall Jon's excellent thread but didn't have time to hunt it down this morning when I posted my response. Thanks for the link to that Jon, AND for taking the time to put that together.

I'm not very good with a multimeter. I think I forgot to state that my dash lights work. I did run a wire direct from battery to each headlight and they work. I don't understand how my park lights work but not headlights. Also noticed 3 wires at dimmer switch but only 2 used. Also turn signals not working. I think the turn signal switch is aftermarket. It is mounted below the steering wheel on the steering column. Trying to not go to a repair shop because it has got to be something simple.

Did you stomp on the dimmer switch? My three wires are: power in, low beam an high beam. Maybe you accidently stopped on the dimmer switch and switched it to the leg not being used?

Dimmer switch needs 3 wires.

1 from headlight switch
1 to low beam on the terminal board on drivers side inner fender.
1 to high beam on same terminal board.

@bucktruck, you need to look at a wiring diagram for your truck HERE and trace the wires to the headlights. The reason the headlights don't work and the parking lights do is that they're on separate outputs from the headlight switch. I don't recall whether the front park lights stay on with the headlights or they turn off when selecting the headlight position.Your '47 should have a fuse for the high beams and one for the low beams, so check whether either of those are blown. A multimeter is easy to use. Just set it on volts and touch one probe (the black one) to ground and the other (red) to each terminal point along the wires. If you don't have voltage coming out of the headlight switch with it pulled all the way out, you've found your issue. If you do get voltage then move to the feed wire on the dimmer switch, then to the terminal blocks on the inner fender. When you no longer get voltage that means the problem is between there and the last place you measured voltage.

Pretty sure the front park light go out when the headlights are on. That's the way my 52 works.

You're probably right, Bill. If they stayed on with the headlights GM could have gotten rid of he 'P' terminal on the headlight switch and connected the front parking lights to the taillight terminal.