Electrical gurus please help.....problem in the lighting circuit
Thread Starter
Safety Car
Joined: Mar 2000
Posts: 3,544
Likes: 448
From: Central Pennsylvania
Electrical gurus please help.....problem in the lighting circuit
I've been chasing an electrical problem on my 1970 for a few years and tonight I think I narrowed it down to the main lighting circuit. As soon as I turn the headlights on (not just the parking lights) the amp guage shows a hard discharge and in a few seconds I pop the fusible link in the heavy 12 ga. red wire near my horn relay. When this link blows the car dies and I have no power to the passenger cabin accessories. I have installed a auto-reset circuit breaker in place of the fusible link because of this problem, so after a brief cool down I can get the car running again.
I've replaced the in-dash headlight switch, the floor dimmer switch, cleaned the bulkhead connector and gave the connections a coat of dielectric, and traced all wiring harness from the starter up to the horn relay and into the dash controls and found no problems with them. What can be the cause of this pain in the butt problem? Does the symptom indicate a short to ground someplace in the headlight circuit?
I guess it's not a ground. If it were the circuit just wouldn't function, right? It has to be a hot rubbing to ground someplace, or a bad connector.
[Modified by ettev, 4:16 PM 5/14/2004]
I've replaced the in-dash headlight switch, the floor dimmer switch, cleaned the bulkhead connector and gave the connections a coat of dielectric, and traced all wiring harness from the starter up to the horn relay and into the dash controls and found no problems with them. What can be the cause of this pain in the butt problem? Does the symptom indicate a short to ground someplace in the headlight circuit?
I guess it's not a ground. If it were the circuit just wouldn't function, right? It has to be a hot rubbing to ground someplace, or a bad connector.
[Modified by ettev, 4:16 PM 5/14/2004]
Racer
Joined: Oct 2000
Posts: 321
Likes: 0
From: Aptos, CA.
Re: Electrical gurus please help.....problem in the lighting circuit (ettev)
Love this stuff. If you've already found a possible cause, you did good. Unplug all the headlamps and try it again. If you have the same problem, it's not the lights, but could be in the wiring to the lights, or even something that's still being overlooked. If it cures your problem, plug in the lights one at a time and see what happens. Hopefully you find the culprit. One important thing, don't try to do a bunch of things at once. Do one circuit at a time or one relay etc. This way you isolate those items and not do a "shotgun" approach.
Drifting
Joined: Aug 2002
Posts: 1,731
Likes: 22
From: Marietta Ga.
Re: Electrical gurus please help.....problem in the lighting circuit (ettev)
Yes, sounds like a short. My '72 wiring diagram shows a common hot wire from firewall out for the low beams on both sides and a separate hot wire for each high beam. When you try the tests check both low and high beams on each side. Look for a crushed wire alone the harness run and around the front lights.
Racer
Joined: Dec 2003
Posts: 275
Likes: 6
From: NY
Re: Electrical gurus please help.....problem in the lighting circuit (ettev)
Totally agree but would add, ALL, lights that come on with the headlights. Tails/sides ,everything. Pull the head light sw. Still blows fuse bad news wiring. Bad because you can't use the load[lamp] to narrow it down. Try pulling/changing EACH wire bundle's position, checking with the H/L sw each time for blown fuse. Now if no blown fuse with ALL lamps pulled, then 1 at a time plug lamps till POOF. There's the short. Good luck
