Here is a link showing the hole in the firewall where the single wire from the light goes thru to under the hood
http://www.cuda-challenger.com/cc/index.php?topic=72062.0It appears that it goes from the dash, thru the hole in the firewall to the black/white wire coming from the switch on the tranny that comes back from the switch to terminal 7 on the bulkhead connector. On the inside of the car 7 goes to the connector that connects the rear wiring harness to the light switch down by your left foot by the kick panel.
If I were doing it, and not doing a resto, I would simply connect it inside the car to the wire going to the reverse lights but, I like to do things the easiest way.
All this light does is pick up power going to the reverse lights when the the reverse lights come on...it is a single wire as the other side of the bulb grounds to the dash. On the inside of the car, I believe it is a white wire with a black tracer that goes to terminal 6 of the rear harness connector.