I haven't done this particular installation but I would assume one of the wire connections would go to a good vehicle body ground. You could find a established ground somewhere under the dash or on or near the firewall or drill a small hole in an inconspicuous solid body metal ( under something or behind a panel) and use a self tapping screw to connect one wire to the metal body. The other wire could be routed under/ behind trim work and into the door frame forward pillar. Remove a door switch and connect the second remaining wire to the wire that hot (has voltage at it) only when the door is open. The other wire going to the switch is the feed and is always hot. The door switch remains electrically open when the door is closed and electrically closes when the door is opened. The switch plunger is pushed in by the closing door to open the circut turning of the dome and underdoor courtesy lights. Alll you will need is a 12V circut tester (a wired bulb) and some type of splicing method. Crimps are quick and dirty and solder and heat shrink is the best. Good luck shouldn't take 10 minutes.