A lot of light switches are situated on the top of the frame above the door in the middle,if the door drops the switch can't close,find the switch and push it in to see if it works,if so place a thin magnet(off a fridge magnet)on the top of the door under the switch,a thin rubbery magnet can be cut into strips until you get the right thickness,otherwise re-align the door.
Rich, August 2008