I agree that it is probably the interlock switch, but since there is also an issue with the interior lights, it may be the "gem module" which manages many functions such as these. If the "door ajar" light is also on when the interior lights fail to go off, it is a sticking switch in one of the door latches. They can be freed-up by liberaly spraying WD-40 inside each of the door latches. Also try www.thedieselstop.com