[dmjlambert]

The light on the truck that shines rearward while you are in reverse is the "backing light" or "backing lamp." I think "backup power" may be an always hot wire that goes to a modern radio that allows it to keep favorite radio station presets. For your backing lights you can send power from an available accessory or key-on fuse like turn signal fuse, and pass it through the switch on the steering column, and rearward to the lights.