The wiring diagram that SOBill did is correct. There are 3 wires on the switch. White/black wire which is hot from the fuse block which passes through the dome light (SOBill's diagram says this is a purple wire but in my car it is white/black). A double purple wire set which is the door switches, and a black ground. In order for the dome light to work when you open the doors, the white hot has to be connected to the purple wire set. When the door opens, the door switch produces the ground and voltage passes through the dome light which makes it light. So if you want all 3 functions, yes, you need a 3 position switch and then play with the terminals to get the right 3 combinations of connectivity.
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