GM Service Manual Online
For 1990-2009 cars only

When a door is opened, the courtesy lamps automatically come on. They make it easier when entering and exiting the vehicle. The lamps can also be turned on manually by fully turning the instrument panel brightness control clockwise.

The reading lamps, located on the headliner above the rearview mirror, can be turned on or off independent of the automatic courtesy lamps, when the doors are closed.