Hey all, first post.... need some help on a rear taillight problem that I'm having trouble with on my 1973 Camaro LT. My passenger side rear signal and brake light have stopped working and I'm at a pause. Any advice is welcome, please see the following:

1973 Camaro LT

1973 Camaro LT

1973 Camaro LT

Dash new bulbs

4 way flashers on... all flash except the rear passenger side.

Headlights on... all front and rear taillights work.

Left signal... driver side front and rear work.
Right signal... passenger front only

Brake light... driver side only

Ohmed right rear light, black ground wire to chassis and have good ground. Checked voltage with hazards on, dark green wire and has no volts. Brown wire has 12 volts when taillights are on. Traced dark green wire back from rear light/harness to harness plug in trunk. Measured and no volts on the dark green wire coming from the front harness with hazards on.

I did open the dash and replace some burnt out dash bulbs. Still have left signal indicator bulb out, right signal indicator working. Could the dashboard harness plug affect the rightside rear flash/brake light? Thanks for any help you all can provide!


Rear passenger signal/brake light socket

Socket

Rear light harness connector plug

 

The green wire controls both the brake and turn signal on the right (passenger) side. The brown wire is the tail lights and side marker lights on both sides and the black is a ground. If you do not have 12V at the socket, you're going to have to trace the back towards the turn signal till you find 12V present. Next, I would check for voltage at the connector in the trunk where the harness splits to go to each side first. If you find no power there, go up to the front and find the harness from the turn signal switch at the base of the column. No voltage on the green wire coming from switch could indicate the contacts in the switch are faulty and the switch may need to be replaced. I would also check the green wire from the column to rear lights to make sure the wire hasn't broken somewhere in between.

 

Thank you Peterpar, is this the connector plug on the steering column that sends the signal to the trunk harness for rear lights? I did have to drop the steering column to remove the instrument cluster. If so, does the signal come from the turn switch in the column, into the bottom plug, then out the top plug to the back harness?

Wiring harness on steering column

 

Yes, I think so. The colors of the wires on the right half of the connector look like what should be going out to the turn signals. The green is to the right stop/turn, yellow is the left stop/turn and the light and dark blues should be the front turn signals. With the key in the on position, engine off and the right turn signal activated, check for voltage on both sides of the green wire in the connector. You should have 12V to a ground on both sides. If not check the blue wires to see if voltage is present. I forget what blue goes to the right front, but one should also have 12V when the right turn signal is activated. If you have voltage going to the front light and not the rear at this connector, that would be a indication that the turn signal switch contacts are bad and the switch will have to be replaced.
Because the stop/turn signals in the rear use the same wire on each side, the switch has to be able to cancel the brake light switch feed when the turn signal is activated on that side. Otherwise, the turn signal would work correctly when activated until the brake pedal was depressed, canceling the turn signals pulsing feed to the rear light with a constant voltage from the brake light switch. The brake light contact in the turn signal switch should always be in a closed position when the switch is not activated. If the contact is damaged and won't close for either the stop or turn function, that would lead to the problem you're describing.

 

Thanks again for your expertise. I'm going to shoot a video on "under the dash Yoga positions" because I have never twisted my body and arms as much as I have working under the dash!

 

Went on to check the connector and measure for voltage at both sides. Good news was I verified voltage coming from the turn signal switch... turn signal, brake, and hazards.... no switch replacement!

Turn signal switch connector

Bad news is to keep tracing the signal path. This is where I noticed a difference in the wires coming from the switch connector and the wires coming to the rear light trunk connector. The rear light connector wires were thinner and had a plastic coated feel.

Wires from switch connector

Wires going into the rear light connector

So there had to be some kind of bridge to connect those to types of wires. I traced the wires from the switch connector to behind the fuse box and found the wire connector with the type that were feeding signal to the rear light connector.

Rear lighting wires from fuse box going to rear connector

I unplugged the connector and measured for voltage at the fuse box and verified all correct volts.

Checking for voltage at fuse box

Then checked for voltage from the other side of the connector and all volts were there.



Went back to measure voltage at the rear light connector, and noticed that the problem switched sides... now the right side was blinking and the left side wasn't working! Went back and remeasured for voltage on the yellow/left side wire and saw volts, went back and the problem switched again... right rear not flashing. It had to be something with the ground, so after checking all ground related wires under the dash both rear signal, brake, and hazard lights now work! Yea! I got to know the nervous (electrical) system of my car well. I then proceeded to replace the dome, courtesy, front signal, side, and rear taillights with LED bulbs. I'll post some pictures of the LED lights later. Hope the dreaded and possessed ground demon doesn't come back! Thanks again
vidkid

 

Posted a reply, but was not published for some reason. So I'll try again...
Found voltage on both sides of the steering column harness connector, good news that I don't have to replace the turn signal switch

Steering column harness connector

Noticed different type of wire from the harness connector and the rear light connector in the trunk so I traced the signal wires into the fuse box and found the plug that ran to the rear trunk connector.

steering column connector wires

Trunk harness connector wires

Plug from fuse box going to rear connector

Check for and found correct voltage out of the fuse box to the wires going to the rear connector. When I went to the rear to check for voltage to the connector, I noticed that the right rear turn signal now worked but the left rear didn't work! I went back and checked voltage again, returned to the trunk and... magic everything worked! I have determined that there must have been a bad ground or moving the connectors completed the circuit. Those bad grounds can really do some crazy things! With that being done, I upgraded my lighting to LEDs... sweet!