GM Service Manual Online
For 1990-2009 cars only
(Dome Lamp Override): You can use the dome override button, located below the exterior lamps control, to set the dome lamps to come on automatically when the doors are opened, or to remain off. To turn the lamps off, press the button to the in position. With the button in this position, the dome lamps will remain off when the doors are open. To return the lamps to automatic operation, press the button again and return the button to the out position. With the button in this position, the dome lamps will come on when you open a door.