if you are talkin about the dome light i think it may get power off the same wires as the map lights. on the driver side pilar(next to the windshield) under the plastic panel i think the wire runs for the map/dome light. what gets me is your wiper problem.
if you take your car to a shop, take it someplace that specializes in wiring, not an audio place. that kind of labor can be expensive cuz it involves a lot of time to test everything. for example, my shop worked on a expedition and put speakers in. one of the guys who put the door panel back on, screwed accidently into the courtesy light wire. it took 4 months for the fuse to pop cuz the screw slowly wore into the insulation then grounded out. the dealer took 6 hours to find it and the total for the bill was 700 hundred dollars, for them to track the wire down and tape it up. have you removed any panels inside the car recently?