Power from Taillight is wired to fuel sending unit... Check!

I have a 65 Dart, its got a 74 power wagon steering wheel (and the same wiring harness).

I'm going to begin splicing this stuff together. My first thought was to see what does and what does not work.

So right now I have:

Wiper motor works great
Fan works great
Headlights, just headlights, no taillights.

My meter tells me that my fuses all have continuity. By the drivers kick panel I have a plug that has 5 wires going in, and 5 wires going out. This is the harness to the back of the car.

Black Wire - Ground?
Purple Wire - Brakes?
Green Wire - Turn Signal?
Brown Wire - Turn Signal?

Dull Blue/Grey Wire - This wire goes to the fuel sending unit, but it gets power when I turn on the headlights, I'm assuming the issue is in the dash wireing harness or maybe in the engine bay. Anyone have ideas on where someone likely would have miswired this?

Also... does anyone have wiring diagrams for a 65 dart? or a 74 dodge pickup truck for that matter?

I just got started on this project.