GM Service Manual Online
For 1990-2009 cars only

The courtesy lamp is located on the headliner just before the front seats. The lamp switch has 3 positions. If the switch is in the center position, the lamp will go ON whenever a door is opened and go OFF when it is closed. In the ON position, the lamp will stay ON until it is turned OFF. In the OFF position, the lamp will not come ON, even when a door is opened.