Hi jumppr,
I don't know which model of Jeep you own...but...
On my CJ, the door pin-switches complete the interior courtesy light circuit to chassis ground when a door is opened. That is: when a door is opened the pin-switch button pops out and the wire on the back end of the switch is connected to the tub.
There is always +12 Volts applied to one wire of the two wire courtesy lighting circuit -- even with the ignition key "Off." A pin-switch merely provides the ground required to complete the circuit.
I added a pin-switch to the tailgate of the Bubbacon by splicing the tailgate pin-switch wire into the existing ground wire that connects to the hardtop dome light.
When the tailgate is opened, all original courtesy lights come on: The hardtop dome light, the two lights under and at each side of the dash, as well as two truck step-bumper license plate lights mounted into the rear speaker enclosures. The latter two illuminate the floor immediately in front of the rear seat.
Piece of cake!
Caveat: The above applies to 1985 CJ-7s. As regards other Jeep models, I don't know.
Regards,
Gadget