The door jamb switches corrode. Only one screw holds it in. Take the screw out, clean the metal portion of the switch (where the screwhole is) and the hole in the door where the screw goes through. Make sure you tighten the screw well when putting it together. Will work fine for a while.
Mine did that 3 months ago, cleaning fixed it, but now it's started up again. Need to figure out a way to keep it clean. Maybe a thin coat of white grease.
