GM Service Manual Online
For 1990-2009 cars only
(Instrument Panel Brightness): This feature controls the brightness of the instrument panel lights.

The thumbwheel for this feature is located next to the exterior lamp control.

Turn the thumbwheel up to adjust the instrument panel lights and return the radio display to full brightness when the headlamps or parking lamps are on. To turn on the dome lamps, with the vehicle doors closed, turn the thumbwheel all the way up.