What triggers the dome and cargo lights to come on? I was naive enough to think it was by door switches.

Drawings of the dome light removal are in volume 1 of the service manual from 8L-151 – 158 - but no mention of trigger switch (other than the ones on the dome light).

The wiring schematic of the dome and cargo lamps is on page 8W-44-2 of volume 2 service manual. Again, no details of any trigger switch.