Does anyone know why auto manufacturers switch ground to the dome lights, rather than switching power? I've been trying to see a benefit of doing that and haven't been able to see one. They did this for decades, and maybe still do, but I don't know why. The reason I ask is I have lights in my doors that take two wires and I really don't want to run power AND ground to the lights, so I'll probably ground one wire inside the door and use a relay to invert the signal to switch +12V to them instead. That's what got me wondering about this.