I have a 1999 Sable and the interior dome light stays on all the time now. A couple of weeks ago it flickered and now stays on. There is no indication that the doors are ajar (no door ajar symbol). The power locks all work from the door button, the remote control and the driver keypad. The two map lights work from their switches as designed. Is there another sensor or is there a control module that controls this light?

 

have you walked around the car opening one door at a time and pressing the light switch to the individual doors? i had this issue a few times and it ended up being a switch out of adjustment...

 

The switches are built into the latches for all four doors. I sprayed WD-40 on each and opened and closed all of the doors one at a time. The door ajar indicator is not showing that any of the doors are not closed.

 

Did you check instrument dimmer control that it is not all the way bright to turn the dome lite on?