I replaced the door on my 1998 Mitsubishi Mirage.

You'll have to check each door switch. Open each door one at a time; locate the switch and try pushing in the switch to see if it turns off. If light is still on, move to the next door and repeat the test. Stop once the light goes out. You've found the defective switch. It would be worthwhile to check if each switch extends as far out as its partner door. (Compare the two fronts then the two rears). If one is shorter, chances are the door can't push it in enough to deactivate it.