New Wire Harness Problems

[Lorne G.]

I just installed a new wiring harness from front to back on my 67. Everything works well except I have no taillights, brake lights or instrument cluster lights.
Thinking it may be the headlight switch, I pulled the switch from the harness and jumped the red and dark green wires and the instrument lights worked. I installed a new switch thinking I solved the problem but with the new switch installed I still have no instrument lights, brake lights, or tail lights. The rear signal lights work so i know the rear harness is plugged in properly.
Any ideas where I should look? I have been pulling my hair out trying to find this gremlin.
Thanks as always.
Lorne

[Jack H.]

Re: New Wire Harness Problems

FYI, GM designers 'featured' a circuit fault detection system.... If there was a DEAD short circuit detected in the car's rear lamps, the circuit breaker (internal to the head light switch) would kick in and ALSO 'kill' the instrument panel lamps to visually 'inform' the driver/operator of a threat to life/limb/property electrical fault in the vehicle...

[Lorne G.]

Re: New Wire Harness Problems

Thanks for this information Jack. Now I know why all indicators pointed to a faulty headlight switch.
If there is a dead short to the rear lights wouldn't the rear signal lights be inoperable as well, as they do work?

Lorne

[Donald O.]

Re: New Wire Harness Problems

Thanks for this information Jack. Now I know why all indicators pointed to a faulty headlight switch.
If there is a dead short to the rear lights wouldn't the rear signal lights be inoperable as well, as they do work?

Lorne

Rear lights are on a different circuit than the rear brake/turn signals. With the power off, check each circuit at the rear lamps to ground, each should show an open.

Don

[Gerard F.]

Re: New Wire Harness Problems

Lorne,

Each of the rear tailights have two elements and two circuits feeding them. The dimmer element works with the headlights and is feed through the light switch. If you have no tailights when the headlights are on, the problem is in that circuit.

The brighter element is fed through the turn signal switch on the column and the switch is fed by the signal flasher, the hazard flasher, and brake switch. Three feeds to the switch.

In the 67 turn signal switch, the brake light and hazard flasher share the same circuity (same tang in the cam), whereas the turn signal circuit is separate. You could have a turn signal flash in one of the rear lights, but no brake or hazard lights. If you don't have hazard flash in the rear, or a brake light in the rear, the problem may be in your turn signal switch.

When you have a turn signal flash in the rear, the opposite side should light when you press the brake. If not, or you don't have a hazard flash in the rear, the problem is probably in the turn signal switch or circuits feeding it.

Hopefully, the problem is in the rear lighting circuit, as it is a PITA to troubleshoot the turn signal switch.

Have fun,

[Lorne G.]

Re: New Wire Harness Problems

Thanks for the detailed information Gerald. This appears to be a bigger gremlin than i thought. I will follow your advise and perform the various tests and hopefully find the problem.
Electrical problems are a real PITA.

Lorne

[Gerard F.]

Re: New Wire Harness Problems

Lorne,

Just saw your other post on the hazard switch. You might try an easy out to get the threads of the knob out from the switch. The hazard switch is a part of the turn signal switch, and if you can't get the threads out you'll have to get a complete switch.

If you get everything going except the brake lights and hazard flash on the rear, yet the front parking lights flash on hazard, it is probably the cam on turn signal switch. Here's what happened to mine:



The inner tang (on top in the picture) feeds the brake lights as well as the hazard flash to the rear lights. As you can see in the picture, the plastic fried around the contact to the tang and insulated it.

The cam is replaceable. Shee-Mar has a new cam out that is an exact replacement of the original. Their part number is SM-15.

However if you are going to all the trouble and have problems with the hazard switch, you might as well replace the whole switch.

[Lorne G.]

Re: New Wire Harness Problems

Thanks Jerry,
The flasher knob has about 1/4" of the plastic rod still sticking out and I can easily screw off the flasher knob but my problem is how do I re-attach the plastic rod to the four way flasher switch? Do I try some epoxy glue? There is not much surface to work with.
Lorne

[Rich P.]

Re: New Wire Harness Problems

For What it's worth I had the excact same problem on a 67 I was working on last August. It wound up being 2 bad repro 67 H/L switches. I had an original laying around the shop so I cleaned it and installed it and everyting worked fine. This may not be your problem but I thought I'd offer the reply

[Gerard F.]

Re: New Wire Harness Problems

Lorne,

Sorry, I must have misunderstood and thought that the knob had broken off and left the treaded portion of it in the hazard switch.

If the broken "plastic rod" is a part of the hazard switch, I don't think there is anyway to repair it. You probably need a new turn signal switch.

Here's an original 67 signal switch for reference (with a broken cam detached):



The hazard switch is on the right in the picture, and is riveted to the switch frame.

I think all of the replacement switches are red, unless you can find an NOS one at big bucks.

[Lorne G.]

Re: New Wire Harness Problems

Rich you may be on to something with the bad repro switches. A friend of mine also bought three to get one that worked. I am borrowing a good original working switch from a friend which will tell me if that is my problem.

Jerry looking at your picture I just might try to epoxy glue the plastic piece back on. i really have nothing to lose since I would need to replace the entire switch anyway. I can't find anyone selling just the replacement four way flasher switches.

Lorne