cornland

I cannot figure out the interior lighting when I open the rear doors (either side) of 1998 GS400. Sometimes the interior overhead lights and the courtesy lights on the door come on, sometimes they don't and sometimes they do after a time. So do I have a bad connection or relay? It isn't the bulbs because the same behavior occurs with the overhead lights and the courtesy lights on the doors. When I open a front door, then the back, the lights all work fine