The door switches report to the CLP ( Central Locking Pump ) which is wrapped in foam under the passenger side of the trunk floor.
It then sends a text message to the BCM ( Body Control Module ) which is in the black box by the battery, that a door or the trunk is open.
The BCM then supplies a ground to the dome light, and if the switch is in the 'auto' position, it will light.

See schematic :