I would splice a trigger line from the wire at the tranny to a relay. The relay should be powered directly from the battery w/30 amp fuse. I would run a ground interrupt switch for the relay ground. This will allow you to turn them off when in town.

Or, you could mount them to the bumper, running a trigger from the back-up lights to a relay, and forget about an interrupt switch. Then mount another light on your roll bar for a utility light.

More than tread lightly. Leave it like you were never there, nor anyone else.
'90 X-cab 4.88's 33 BFG AT's, rr ARB, Headers, Ignition upgrade, cold air induction.
'91 X-cab 5.29's 315's BFG MT's, rr ARB, custom bumper and flatbed