Frustrating wiring issue, turn signals brakes, and tail lights, 1980

[Ron Dame]

With the headlights off, all lights work normally.

With them on, there is current back feeding to the right signal indicator on the dash, and sometimes the right brake light works, sometimes it does not, but only when the headlights are on.

I cleaned both front and rear light sockets on the right and used dielectric grease. The ground on the front was confirmed with almost no voltage drop. The back socket where it connects to the light body is clean and greased, though I don't think this is the primary ground, if any ground at all. I ran a temporary ground from the right light socket to the left (which acts normally) but this did not solve the issue. I've attempted to find the proper ground for the RR lamps, with no avail.

What am I missing?

 

[ronmanfredi]

Are you saying that all lights, run, turn, brake, reverse, everything works perfect when the headlights are off?

[Skip Lackie]

You have already properly diagnosed the problem -- just haven't found it. There is a bad ground somewhere, probably in the headlight circuit.

[Ron Dame]

Thats right Ronmafredi. All is normal until I turn on teh headlights

[Ron Dame]

HI Skip, that makes sense. If it only happens with teh headlights on, it makes sense that's where the bad ground is. It does seem odd that impacts only the right rear brake light though.

[ronmanfredi]

2 hours ago, Ron Dame said:

Thats right Ronmafredi. All is normal until I turn on teh headlights

Disconnect both Headlights and then see what happens.  If everything is good, then connect one of the head lights and check again.  If one headlight / circuit is causing the problem then you will be able to discover which one.  If one is the problem, then swap headlights just to eliminate a bad light.  If the problem remains on the same side, then it's time to check that side wiring / ground circuit.  

If disconnecting the front lights don't make any difference, then I'd be looking at the headlight circuit wiring for problems.

[Ron Dame]

Well, I found the offending ground, and it was the right front turn signal. I had only looked inside the housing and at the pigtail, ASSuming that the ground wire was directly at the socket, not on the outside of the casting.

I had a minor fender=bender last year, and it appears the body shop lost the correct screw for the ground and used a long sheet metal screw instead... so long, that the wire was loose. Worse, it was a much larger diameter that needed and split the lug on the housing.

For the short term, I found a shorter, similar thread screw and have things operational until I figure out a way to properly repair the lug or create a different ground. I'm thinking of trying a dab of Frost King defroster repair epoxy which is conductive, to repair the lug.

[ronmanfredi]

I had the same problem with one turn signal and just re-soldered the ground wire back to the back side of the bulb holder.  You'll need to clean the metal good and then use flux with the solder.

[DaytonaR2]

The two wires are swapped on one of the turn signals.  Which creates an improper ground