Since its not something from the factory…no one knows what wires the installer tapped into. Unless you pull back the headliner to follow the wires…try the process of elimination.
I would check everything that is in the overhead console area to see if anything else is not working. That could be an indication of what the installer tapped into….and possibly what fuse to check.
If it was connected to something that was switched…perhaps they tapped into the HOMELINK wiring (which requires that the ignition is on…or in the case of BMWs with START button…that the START button has been initiated).