My '02 Tracker doesn't have a "Door Ajar Light" that I know of. However, right after I got it, I noticed that every time I leaned on the driver door armrest, the dome light would come on. It turned out being the three (I think) screws holding the latch mechanism on the driver's door were so loose that the whole thing could wiggle around. I tightened them up nice and snug, and it's never done it since (two years later).
Otherwise, it could be a wiring thing, and those are no fun to diagnose . . .
Good luck.