If you do have cab lights, I would agree with Arctic Fox. Water runs down hill so if you have a leak in the roof it very well could be running into the areas you describe. Disconnect the moldings around your inside roof covering and gently pull down until the cab wiring is exposed or better yet just replace the cab lights and/or seals and wait and see. If it is the cab lights, I would suggest airing out that area until dry, to prevent mold from forming.
1994 F250 HD, IDI Diesel, 3:55 gears, K&N filter, Hayden Tranny Cooler, Monroe HD SensaTrac shocks, dual pillar pod with temp & tranny guage, poly fuel tanks,aluminum racing radiator