GM Service Manual Online
For 1990-2009 cars only

The interior lamps control is located on the overhead lamp. To change the interior lamps setting, slide the switch to one of the following positions:

OFF:  Turns the lamp off.

ON:  Keeps the lamp on all the time.

Door:  Turns the lamp on when any door or the liftgate is opened. The lamp goes off when all the side doors and the liftgate are closed. If the lamp switch is in the door position and a door is left open, the lamps will go off automatically after 20 minutes.