[38932]

Huge issue with tail light, turn signal and brake light on driver side rear in my '65 GTO. Changed the light socket and bulb 3 times. When the bulb is in the socket the grounding strip on the socket has power and should be ground.

The passenger side works as it should. Front parking lights, turn signals, and headlights operate with no issues. In addition I had no instrument lights before the tail light fuse issue.

Disconnect the ribbon harness at the fuse box to eliminate the tail light issue.
When I turn the headlight switch on the tail light fuse shorts.

The brake light switch is working, this is a tilt column and the switch is working. I have blown a flasher and replaced it and now the driver side indicator light is not flashing, just lights up as if the bulb is out.

The whole deal seems to be getting worse. Could be corrosion, connections, but appears there is a dead short when the headlight switch is on. I have tried 4 headlight switches. Any ideas?

[Pepi]

Improper bulbs somewhere? Just a thought.

[rexs73gto]

Sounds as if you have a wire either put in the wrong spot or a wire has burned through & it is touching another hot wire & when you turn on the headlamps your getting power where your ground should be.

[38932]

I checked the bulbs, no issues.

The problem was intermittent but now appears constant. I thought the same as a wire was in the wrong place but your comment about a wire touching another sounds more like it.

[Peter Serio]

Just a thought, you say at first the problem was intermittent but now it is constant. This is actually a good thing. If I were there what I would do first is try and isolate the problem. First verify the issue then one at a time un-plug the various branches of the harness looking at the one disconnect where the problem suddenly goes away.

Then at least you have an idea of where to investigate.

[38932]

It appears the power feed to the dash and tail light is the main problem (dark green). This was the intermittent problem, no dash lights. Then they started working but still had power back feeding at the tail light ground.

Now the fuse just blows if I try the headlight switch. Good idea and I will be back at it.

[LPete]

I don't think you have power backfeeding at the ground -- you just don't have a good ground. If you take the bulbs out the "backfeed" is gone, right? If the ground is good you can't have voltage on it.

[kate`s67gto]

Replace fuse and just step on brake pedal. Brake lights yes or no on both rear lights? If no fuse failure?

[LPete]

A handy way to troubleshoot a fuse-blowing problem (so you don't end up with a pile of blown fuses when you're done) is to take a light bulb (I use a headlight with leads and alligator clips) and wire it in place of the fuse. When the problem is occurring the light will be on full-bright, and when it goes away the light will be dim. This lets you disconnect and wiggle wires and immediately know if you've isolated the problem without replacing and blowing another fuse.

Does this car have a separate fuse for the instrument lights? If it does, and it's not blowing, the problem isn't in the dash lights.

How are you determining that you have power on the ground side of the bulbs? If you measure with a voltmeter, and don't have a good ground to the taillight, you'll measure battery voltage. If you use a test light with an incandescent bulb (so it draws significant current) you'll see that the lamp isn't full brightness, because it's in series with the taillight bulb.

[bob d]

here's a long shot. I had light problems and it turned out to be the floor high low beam switch was rusty and corroded. bob.

[38932]

The driver side tail light has power to the ground strap when the bulb is in it. The bulb is completing the circuit. Put the bulb in it lights without grounding. Take the bulb out no power. The other tail light works only when grounded.

Brake lights, signal and running lights only work on passenger side. Brake light switch is working.

The car has a separate fuse for the instrument lights. They work through the tail lights and the fuse only has power when the tail lights are on. I will try the voltmeter on the tail lights but the test light was bright. I like your headlight tester idea as I am depleting the worlds fuse supply with this issue.

Today I took the harness apart, in the car mind you, no issues found. I have isolated the harness down to the fuse box and dash. Disconnected the turn signal switch and ribbon harness. Changed out another headlight switch, still blows the fuse. Got to be in the dash circuit. High beams and headlights work.

[LPete]

That ground isn't grounded. Fix that, and it'll take care of part of your problems. It won't fix the fuse blowing issue.

Take a wire and run it from a good ground to the ground strap and you'll see what I mean.

[38932]

Pulled the tail light fuse and used the headlight as a tester. I have isolated the short down to a natural wire from the headlight switch. When I shut all the doors the headlight turns off. It also dims and brightens with the rheostat so it works as a dome light. Confusing, since this is working through the tail light circuit.

When I pull the natural wire the short is gone but dash light circuit has no power.

My switch has 2 natural wires. All the wiring diagrams I looked at show 1 natural wire which I know operates the courtesy lights. The short is in the additional natural wire that is not shown on the wiring diagram.

It appears a wire is crossed somewhere and this could have been an existing problem as I just restored this car using the clean and uncut original harness. The fuse box needed attention but is working. Hate to buy a new harness, might need to trace each wire.

["QUICK-SILVER"]

Any updates on this?
What you are describing, in your last post, sounds like the spring or a component from the rheostat (dash light bright/dim) has come lose and is making contact with the dome light 'ON' ground contact that is also one of the functions of that part of the headlight switch.
If it is a rheostat component broke, that would explain loss of power to the dash lights.
The bright/dim on your test light, when turning the rheostat up and down, sounds like its showing dome light voltage. Or comparing voltage between the dome light and tail light power supply.
Pretty sure the headlight switch has to be mounted for the ground, dome light 'ON', to work.
Really hard to say on this one without a few more details.

[38932]

At this time the dome light circuit is working. This issue might have been a ground problem. My harness is very nice, no cuts or repairs. The dash lights did work

Well I discovered today that the brown tail light wire is always hot. I found when the headlight switch is connected to the plug the brown wire has power. The problem is that the headlight switch in not pulled on. For example, the license plate light is on and the headlight switch is off.

So when you pull the headlight switch to turn on the tail lights it shorts the fuse. I discovered on the fuse box tail light circuit without using a fuse that both sides of the fuse contacts have power. Some how another circuit is powering this. I checked from the brown wire to see if another wire had continuity but did not find any.

I have purchased a new headlight switch but it did not fix the problem. In fact this issue is shorting the headlight switches. I have bench tested the headlight switch by checking continuity.

The dash lights are energized through the tail light circuit so something is preventing that connection.

["QUICK-SILVER"]

Check for continuity between the brown wire terminal and the natural wire terminal on the headlight switch. Do this with the wires unplugged and try turning the headlight knob while testing. There shouldn't be any continuity between the two, unless the rheostat for dash lights and the dome light ground contact have gotten shorted together somehow.
A short in that part of the switch will cause ALL the symptoms you're getting.

[38932]

Removed the dash harness, did another inspection and continuity test. Looks good, re-installed harness double check for shorts, install new headlight switch. Dash lights are working, no short. Possible bad switch but I had 8 switches to test from.

Check courtesy lights, found a short through the screws when attaching to headliner, what else could go wrong.

Everything back together and working except brake lights. Testing brake lights, now this has morphed into turn signal problem. Try left signal and right front is flashing, tail lights work, parking lights very bright as if too much voltage.

Chasing a demon in this car, possible voltage regulator, all ground appear good, who knows. Always interesting trying to get a frame off car back on the road.

[kate`s67gto]

The steering column can will cause short in tail lights. If it is a tilt column they have been known to chafe the wiring in the column. Also check the brake light switch wire lead for chafing. Ask me why............. It could also be the turn signal switch remember signal lights over ride brake light on the side your turning.

[38932]

I believe I have fixed the problem after 3 weeks of testing and getting advice from this forum. I thought it was one issue but really was a number of issues that appear after you find one fix. Here is a list of what I found:

Bad headlight switches, bought new but I still believe something was shorting the others. Can you actually have 8 bad used switches?

Bad tail light sockets. They look and appear to work, but they don't.

Bad parking lamp sockets, not just grounds, bad sockets. Tried 2 used before I found a good one.

Bulbs that work for a while then go bad. Turn signal switch that works, then after repeated used fails on one side. Bought a new switch and bulbs. Try to find an 1157 amber, you will find one after going to 3 parts stores.

A fuse box that shows power at the fuse but not to the circuit. So, the fuse indicates power but due to age, corrosion, it is not feeding beyond the contact.

Anyway, this was a learning experience. After 8 1964, 1965, and 1967 GTO restorations you think you have experience. This was an experience and I hope I am not speaking too soon.

The best tool you can own is a test light that detects power and ground to a circuit.