The switch is only in the dome itself, to the interior light you have a ground, constant positive, and a switched(by opeing the doors) positive.
This way the ground is always the same, however when you shut the switch off none of the positives will make it to the bulb, when its on auto the switched positive is hooked to the bulb so when the door opens the light works, and when the on position is selected the constant positive is used to power the bulb.
I would say the best thing is if you only need them off for detailing is to pull the fuse, however on mine they do shut off after 10 minutes of being on constantly without the engine running.
