My 69 cutlass right taillight was dimmer than the left. I assumed it was a grounding issue. The left side socket is a three wire and the right has only 2 wires. I thought that meant the third wire on the left light must be a ground and the right side grounded on the housing. I turned on the lights and pulled the right light and socket out of the assembly and it stayed on. That can't be right. I put it back in and then When I pull the left socket out the left light goes out. This can't be correct. What is that third wire for on the left light ? How can the right light stay on without a ground? Other than dim on the right light the lights work as they are supposed to .

 

If you mean that the LH socket has one yellow and two brown wires and the RH socket has one green and one brown wire, that's normal. The brown wire is the tail light feed from the headlight switch. It runs down the LH side of the trunk to the LH socket, then out the LH socket to the other side of the car. There are also splices that come off the brown wire for the side marker and license plate lights.

 

Ok that makes sense but should not the RH tail light go out when I pull it out? The green wire seems to be grounding it because when I disconnected it it went off.

 

Go pull the socket out again and look closely at the bulb. Notice that BOTH filaments are lit, not just the one for the taillights. This is because by removing the ground path, the circuit now grounds through the brake light filament and into the brake light circuit. Have someone step on the brake pedal and both filaments will go out.

For even more fun with electricity, get a jumper cable or wire and run it from one of the metal grounding tabs on the socket to a good ground. Notice that now only one of the two filaments is lit. The brake lights will now work correctly as well.

 

Thanks joe.