Interior Light Wiring Issue - 69 Barracuda

Yep.

The map swich just passes the ground signal from the yellow door switch wires to the brown which gives the map light a completed circuit. When the switch is flipped it shorts the brown to the switch case completing the circuit to ground. As pointed out by others before it can be a battery killer when left on. You can bypass the switch by connecting the brown to yellow then the map light will only function with a door open or headlight switch twisted to the dome on posistion.