Hello.

I'm sure that you've already thought through how actually trying to pull a trailer with a 40+ year old unibody car is probably going to pull the car apart, so, we won't need to get into that.

The easiest way to do it would be to buy another taillight harrness, butt-splice it into the taillight harness of the car, color to color, near one of those clips that holds it onto the lip of the driver's side of the trunk opening, clip the wires on the rearward side of the new taillight harness, and attach the appropriate plug connector for the trailer lights to the rearward end of the new taillight harness.
