The switch on the dome lamp has three positions.

(Off): This position shuts off the lamp completely, even when a door is open.

(Door): This position makes the lamp come on whenever a door is opened.

(On): This position turns the lamp on, even while the doors are closed.

Your dome lamp may have two rear reading lamps. See Rear Reading Lamps

For vehicles with a dome lamp, move the lever to change the setting.

(Off): Turns the lamp off, even when a door is open.

(Door): The lamp comes on automatically when a door is opened.

(On): Turns the dome lamp on.