The interior light in my 2004 F150 flickers on and off. I can slam the drivers side door and it may do it a couple more times then quit. Or if I'm driving slow over a rough spot in the road it will flicker on and off. I sprayed about a half a can of WD40 into the door lock mechanism in the door but that didn't help. I also took the door panel off to see if i could locate the door switch itself but i didn't know exactly what i was looking for so i never pin pointed the switch. Is this a switch problem or possible interior light relay? I'm assuming door switch since slamming the door seems to help it. Exactly what am I looking for and where inside the door? Thanks