Trailer Wiring?

[Honest Bob]

Hey guys I'm wondering if anyone can identify or have any theory's on this wiring on my '75 GMC C35 2wd. I'm having a hard time identifying if it is oem and its purpose. I'm guessing its towing/cap related but I'm not an expert in that area.

Both the red and the green/white/black/darkgreen run from the engine bay and Y off right where the cab and bed meet and then continue to the rear bumper.

I dont seem to be getting any pixies out of any of the wires and I want to get a class V tow hitch and trailer wiring setup. I wouldnt mind reusing the wiring if I could as it seems like oem or somewhat professionally installed.