[64Lemans]

Hello.
I've been working on fixing the wiring for the front end for some time now. I have finally gotten to the point where the parking lamps are working. Parking lights are on... directional works...the correct filaments are working when needed, etc... I replaced the headlight switch which solved most of my issues.
The passenger side marker light is lit...and works great. The only remaining issue I have is the driver side marker light. I know the socket and bulb are functional as ...when I was switching wires around, the light came on. But when I have the lamp / directional working the way it should, the marker light will not light up.
Looking at the wiring diagram, it looks like one wire is power and the other is going to the headlights. Is this a ground of some sort or ? Wondering if I could use the power from the parking lamp if needed. Any suggestions would be greatly appreciated. Thanks....

[JLMounce]

It's going to be a poor or non-existent ground somewhere. All of the lights up front are grounded to the same circuits.

If you're chopping into wires, re-arranging a bunch of stuff and fighting this, I'd highly recommend a new forward light harness. They are readily available, plug and play and aren't too expensive. If you've got enough going wrong there with the lights, I'd do the engine harness at the same time as they both exit the bulkhead connector.

Like you I fought lighting wiring for a long time. Putting new wiring in the car was one of the best things I did from a reliability and ease of use standpoint.

Edit: I should also point out that the bulbs themselves are part of the ground circuit. The bulbs ground to the contacts in the sockets and the sockets will also typically ground to the lenses (this may not be the case for the markers). If the bulbs or sockets aren't grounding properly, that will also cause the issues you're seeing.

[north]

Unlike the fullsized cars and the LeMans and Tempest models in 69 the Firebird and the GTO need a ground wire for the parking lights because of how the housings are designed. The black wire in your diagram is the ground wire (the three black tapered dashes are the symbol for ground connection).