1968 1200C Tail Light issues

MASTERSTAKE

New member
Alright,
I have a 1968 1200 C pickup that until yesterday had all the wiring fixed except the fuel gauge. I think what happened is while I was rummaging around looking for the fuel gauge wire/connector I knocked something lose/ unplugged something because now I have some serious electrical issues.

The Issues: Brake lights do work, but that's about it, the backup lights are doing just fine and have been disconnected so I don't get any interference from there. Firstly, the turn signals turn on both tail lights and flash them as if the hazards are one. However, the hazards are not on because it blinks properly upfront. In fact, all the lights for the front of the truck work perfectly, and only the rear lights are affected. Secondly, although the voltmeter reads 15 volts at the light plug when the tail lights are on, the bulb doesn't turn on. Most confusing of all is when the taillights and the turn signal are on at the same time the bulb lights up without being grounded. I know this because while testing theories as to why we had these problems I thought that perhaps putting the light bulb in and twisting it into place was making the contacts touch but when I tried it the light bulb turned on without being grounded to the frame.

Now, this sounds crazy and I would agree since none of these problems seem to be possible in the first place, but I have checked the entire wiring harness from the firewall out for continuity and for frayed/damaged wires that could cause shorts and there is absolutely nothing wrong. In fact, when you just measure with a voltmeter (and I do know how to use one) you get good numbers on all the contacts e.g. tail lights when on: 15 volts, Turn signals when on: alternating between 2 and 15 volts. and when I press the brake voltage goes on solid on both left and right contacts. Both me and my dad have worked on this for several hours and while all the numbers check out and make sense when there is no bulb in. As I said before all the wiring outside of the firewall looks fine and checks out so I think the problem has to be with the turn indicator relay, hazard light switch, and the brake lights (I forgot to mention before but when you push the hazard switch in the tail lights come on even when the hazard fuze is out) which seems to tell my that there is some sort of back feed issue somewhere under the dash.

Sorry for this longwinded explanation but I hope someone can help me. While I'm not the best with electrical I at least understand the basics and at the moment I am completely stumped as to what the actual cause of my problems is.

Thank you,
Travis
 
My initial concern would be with seeing 15 volts of resting surface charge anywhere. A sound and fully charged battery will generally display 12.6-8v an hour or more after being replenished. A reading taken while the engine is running will commonly display between 13 to 14.5v with normal alternator function. Readings much above there indicate potential overcharging.
Now to your specific issue...I would check your firewall bulkhead connector that contains the circuits for the rear harness. Make sure there's nothing janky going on there. Another area of suspicion could be your turn signal switch. The internal contacts could be compromised by gook and grime. I'd also examine your fuse block to make sure that all of the fuse sizing is correct and that no fuse prongs are inadvertently touching any adjacent prongs.
 
My initial concern would be with seeing 15 volts of resting surface charge anywhere. A sound and fully charged battery will generally display 12.6-8v an hour or more after being replenished. A reading taken while the engine is running will commonly display between 13 to 14.5v with normal alternator function. Readings much above there indicate potential overcharging.
Now to your specific issue...I would check your firewall bulkhead connector that contains the circuits for the rear harness. Make sure there's nothing janky going on there. Another area of suspicion could be your turn signal switch. The internal contacts could be compromised by gook and grime. I'd also examine your fuse block to make sure that all of the fuse sizing is correct and that no fuse prongs are inadvertently touching any adjacent prongs.

Thanks, I have pretty much nailed down the turn signal switch as my issue. I haven't opened the steering column yet to check it but I have traced wires and looked at all the different plugs and all that seems just fine.
 
Back
Top