Possible headlight relay gremlin?

[71roadunnerWI]

Hey guys, I'm new here and I'm not sure if anybody else has had this issue. I bought the headlight relay harness from crackedback it's a thing of beauty. I've been trying to contact him via email, but I haven't heard back from him yet. The headlights worked as normal before installing the harness. I hooked up his headlight relay harness with the ignition off the headlights work normally both low beam and high beam, but when I turned the key to the Run position the headlights come on low beam only and the high beams come on if I hit the switch. Does anybody here have any idea what would cause this? My grounds are good and clean. Somehow with the ignition on its powering up the relay harness and the headlights turn on. Any help would be appreciated it's a 1971 Plymouth Roadrunner

 

[gtx6970]

Where do you have the main power wire connected?

 

[71roadunnerWI]

Where do you have the main power wire connected?

I have it connected to the alternator per crackedback's instructions. Before installing the harness the headlights worked as normal somehow someway with the ignition on it is powering up the relays and turning the headlights on I am baffled on this one

 

[451Mopar]

Any unusual dash lights like high beam or brake light? Bad ground might be causing lighting harness to try grounding through the relays? Could also be a bad light switch.

 

[71roadunnerWI]

Any unusual dash lights like high beam or brake light? Bad ground might be causing lighting harness to try grounding through the relays? Could also be a bad light switch

Any unusual dash lights like high beam or brake light? Bad ground might be causing lighting harness to try grounding through the relays? Could also be a bad light switch.

That's what I was kind of thinking. The new relay harness is grounded properly. My guess is it's either the headlight switch which I replaced probably 25 years ago because when I got the car to turn on the headlights it was wired to a household light switch. Or it's a bad ground somewhere else. The headlights work normally without the relay harness hooked up, but my guess is it doesn't take much to trigger those relays. I have a new Dash harness that I will be putting in this winter. I plan on pulling out the steering column and dash. To call my current Dash harness of bird nest is an understatement. I was just hoping it would be something simple that I'm missing. Because me and electrical stuff do not get along I dread any electrical work.

 

[71roadunnerWI]

That's what I was kind of thinking. The new relay harness is grounded properly. My guess is it's either the headlight switch which I replaced probably 25 years ago because when I got the car to turn on the headlights it was wired to a household light switch. Or it's a bad ground somewhere else. The headlights work normally without the relay harness hooked up, but my guess is it doesn't take much to trigger those relays. I have a new Dash harness that I will be putting in this winter. I plan on pulling out the steering column and dash. To call my current Dash harness of bird nest is an understatement. I was just hoping it would be something simple that I'm missing. Because me and electrical stuff do not get along I dread any electrical work.

I forgot to answer your other question. All the other lights work normally before I installed the harness just like they did when new. Once I installed the harness and the ignition goes to the on or run position just the headlights come on nothing else. If I pull the headlight switch with the ignition on then all the other lights come on as they should somehow some way something's triggering those relays with ignition switch on.

 

[451Mopar]

You could put an amp meter in-line with the relay trigger to see if and how much current flows to the relay?
I would unplug the headlight switch and see if the problem still exists. I think it might not be the switch, but grounding of the dash lights or some other problem?

 

[Belvedere408]

I also had an issue on my 65 Dart on a cracked back harness. When I plugged my harness in I could only get the brights to work properly. My wiring is 60 years old I pulled the relay harness off and my lights work fine. I figured I had some bleed off on some my old wiring that was magnified by the extra power.

 

[71roadunnerWI]

Thanks guys for replying. I got a hold of Rob and he had to try a couple different things nothing seems fix the problem yet. When I unplugged the trigger wire the lights do not light up when the ignition is on which is the problem. I'll try and unplug the headlight switch it seems like a real pain in the butt to get to and I will also hook up an amp meter to the existing harness to see if there's anything bleeding through. I replace that headlight harness probably 15 years ago I bought it from Year One the car is always kept in the garage and in the last 15 years if I put on 10,000 miles it's a lot so I'm assuming the harnesses in good shape and not the problem.

 

[451Mopar]

I was thinking if the high beams came on, the dash might be grounding through the high beam indicator light, but since it is low beams turning on I think it might be the light switch?

 

[71roadunnerWI]

I was thinking if the high beams came on, the dash might be grounding through the high beam indicator light, but since it is low beams turning on I think it might be the light switch?

I will be digging into it this weekend and keeping you posted. Crackedback harness is great and I'm 99.99% sure that's not the problem. The birds nest of dash harness is most likely the problem. Couple years ago I bought a year one dash harness I was planning on installing it this winter. Looking at it last night there is a ground pigtail that comes off the harness on the driver's side near the kick panel. I'm going to check and make sure that is connected and then I will unplug the headlight switch and see if the problem persists. I would assume if I disconnect the headlight switch and the problem goes away it's in the switch itself. That switch was probably replaced 28 or 29 years ago because when I bought the car believe it or not to turn the headlights on was wired to a household light switch.

 

[Plymouth71]

So???? Where you at? Did you solve the problem?

 

[71roadunnerWI]

Hopefully I can work on it more this weekend. Its been a busy summer for me. I cleaned all my grounds and going to try and disconnect the headlight switch to see if that's it. I dont know what else it could be. This winter I will be replacing the dash harness. If anyone has any other ideas chime in.

 

[Crackedback]

Bad memory here... On the relay harness wires to the alternator, both are hooked up to the same charge stud, correct?