GM Service Manual Online
For 1990-2009 cars only

The inside rearview mirror has a switch located at the center of the mirror to enable or disable the automatic day-night feature. With the ignition in the ON position, depress the switch to enable the automatic day-night feature of the mirror. A green indicator will illuminate on the mirror when the automatic day-night feature is enabled. To disable the automatic day-night feature of the mirror, depress the switch.