Technical Headlight Wiring Help

Ok, I have a 49/51 F1. I rewired the whole truck. I just put the front end back on and working on headlight wiring. It's a simple setup. No relays, just direct from switch.

I wired up the left headlight socket plug first.
With the test light, I test the socket plug. Everything checks out fine. Turn on low beams, the low side has power. The high side does not.
Hit the high beam switch and the high side has 12 volts, the high beam indicator light lights up and the low beam side has no power. I think....ok, everything seems fine.

As soon as I plug in the head light and pull the switch on, both sides are getting power and the high beam indicator stays lit in both positions.

What am I getting wrong? It's a new headlight btw.

 

Sounds like your dimmer switch is bad or it’s feeding back for some reason…do your testing at the dimmer switch first…power in and then it should split the power to each headlight…low beam and then high beam…completely separate coming from the dimmer. The high beam light is connected to the high beam side of the dimmer switch.

 

do you have the ground wire to the headlight connected to ground?

 

Head lamp socket wires not in correct positions

 

Yes and when I used the test light I had the ground clamp in the socket ground.

 

I tried reversing them , same results

 

I tested at the dimmer and that seems to be working correctly.
One question I do have is, Once I put power to the dimmer, Does it matter witch side I tap off to go to the low and high? I mean, I didn't think it would matter but if it does , I could try reversing them

 

Question first. How did you get your high beam wire for dash indicator lamp?

 

How does one reverse 3 wires?

 

It shouldn’t matter as long as the wires going from the dimmer to headlights are in the correct positions…activate the dimmer and test both plugs to make sure they match…you have three tabs on the headlight…one is ground, one is low beam and one is high beam. Be sure the wires are in the right position on the plugs to the headlights…putting power to the ground tab will cause a feedback…check it out. Sometimes a dimmer switch will go bad internally and cause a feedback…you may need to jumper around the dimmer to be sure.

 

Well I figure the ground stays put in the center of the plug and I tried switching the other two side to side. Unless I misunderstand what you are saying.

 

I think ground is one side, not the center terminal...might take a close look in the bulb, as to how the filaments are wired.

 

Jim is right, you've got the ground mixed up. Looking at the back of the lamp with the single terminal pointing 'up', the left terminal is ground, the top one is low beam, and the right one is high beam.

You can verify this with an Ohmmeter. With your meter set on its lowest range, measure and record the results between each pair of terminals. Two pairs will read roughly the same, the third pair will read about double. The terminal you didn't read to for this measurement will be the ground.

 

Yes! I went out and rearranged the wires and bingo! It all works as it should. I screwed up by thinking the center post was ground.
Thank you to all that replied and made me rethink my steps to get the problem solved.

 

Thanks for coming back and posting what cured it!

 

If you want to run some protection on that circuit. I can help out. Just let me know.

 

Thank you. I have fuses on everything. I'm hoping that's enough?

 

Yeah, kind of embarrassing. I rewired the whole car, not with a kit but, by rolls of wire and fuse boxes. I researched everything...wire sizes, fuse sizes, everything. And I got hung up on the head light plug . lol

 

The most important things is 1) you learned 2) you fixed it . The good Lord above is the only one I know that is perfect 100 out of 100 times.

 

oh yeah, you’re good

 

x2 on what 41rodderz said. And even very knowledgeable and experienced people make mistakes. One of the best small block Chevy engine builders I ever knew was stumped as to why he wasn't getting fuel to the carburetor on a freshly built engine with a new AC fuel pump. Until he spotted the fuel pump pushrod laying on his workbench.

 

Ground…..ask me how I know….

 

Ask me how I know you didn’t read the whole thread.

 

Absolutely right,I didn’t read the whole thread. I had that same problem on my avatar while adding fenders. I couldn’t believe the headlight bar wouldn’t be a good ground.

 

Thank you. I save pictures like this for future reference. Just in case.

 

Another option. Probing or checking headlamp prongs is another way to find ground prong. Touch one prong and hold constant contact to it then touch the other two prongs for continuity. If both of the other two prongs do not show continuity try another prong to hold constant contact with (then one more if need be) until you get continuity reading on the other two prongs. The prong that you've held constant contact with will be the ground. Providing the lamp is in good working order that is.