GMC 2000 Savana - Manual (Page 118)

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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.
If the DOME OVERRIDE button is pushed in, the dome
lamps will not come on.
If the DOME OVERRIDE button is out, your interior
lamps will work as usual.
If the button is pressed in, the interior lamps will not
come on when any of the vehicle’s doors are open. This
feature is helpful when you want to leave your door(s)
open for an extended period of time and do not want to
run the battery down. The button is located next to the
lamp switch.
Reading Lamps (Option)
If your vehicle has reading lamps, press the button next
to the lamp to turn the lamp on or off.