I would suggest you may have a problem with the door switch or associated wiring, which could make the lighting system think the door is open all the time. If this is the case, the light would go off after a while and would not come on when you opened the door again. But if it's coming on when you open the door ( i would experiment by only opening the door you were working on previously ) and then not going off, I guess there could be a problem with the timer / relay which controls the lights. They should normally stay on for a bit after closing the door, by the way, they don't go straight off.
* Edit... but you say you already played with the relay. Anyone know if that relay only controls the door switching? Or should it not kill the interior lights altogether if you pull it?