Power comes directly from the battery on a fused line - through the switch (it's LED so I wasn't worried about burning out the switch, hence no relay) and out to the back - ground comes from the taillight ground and I have another switch in the rear so I can leave it on inside the cab at night and be able to switch it on and off from the camper.
The only things I did different from just drilling a hole and tightening the lamp assembly was to cut out a gasket for the outside hole out of mountain bike inner tube (there was an old one in my toolbox) so I didn't mar up/crack the exterior, silicone to seal it up and swap the regular hex nut for a nylock nut.
That's a little temporary - I'll build a switch box for it later on in the springs once it warms up here.
The light only gets used around camp set up time - I don't use it so much for backing up anymore as I've switched the truck from an 09 Tacoma access cab to a 2010 double cab tacoma and the backup cam works wonders.
