rear ground wire 69 dart.

Snake-
The "ground" for the tail lights and the plate light comes from the fact that the light housings are grounded to the body. The light sockets for the tail lights have metal feet that retain them to the back of the light housings, and provides the ground.
The plate light is grounded as it is mounted to the metal rear bumper.

The original harness wasn't wrapped in tape, but rather snaked through a black weaved cloth like covering.

If you need a picture, please ask.

George