Originally Posted by Shamrock

The switch on the courtesy light is a 3 position switch. Looks like the dome light and cargo light operate in parallel. Position 1 keeps lights ON all time, Position 2 lights are controlled by the door switches, Position 3, keeps lights OFF all the time. If the cargo lamp is ON all the time, but the dome lights operate normally with the opening and closing of the doors, then there as a problem in the wiring --- possibly a short to ground. See Page 8W-42-2 in the service manual for a schematic of the wiring for the lights. (Service manual in PDF form is available on this Forum)