1997 Chevrolet Express Van Owner's Manual - Page 102

Reading Lamps (Option) You can use the DOME OVERRIDE button, located below the headlamp knob, to set the dome lamps to automatically come on when the doors are open, or to remain off. To turn the lamps off, push the button once. With the button in this position, the dome lamps will remain off when the doors are open.To return the lamps to automatic operation, push the button again and return it to the "out" position. With the button in this position, the dome lamps will come on when you open the doors. If your vehicle has reading lamps, press the button next to the lamp to turn the lamp on. Press the button again to turn the lamp off.