Thanks for the responses, I have been doing a bit more research, and some testing. The only references I could find about that wire were in reference to car alarms, and multiple people post that you need a relay to use the wire. And as I assumed the wire was sending a low voltage signal to coordinate the dome activity, a relay made sense.
Upon inspection, I found the wire in questions probably acts as a ground, having lower voltage than the power wire. It looks like it may be the same wire actually running to the dome switch, but I dont get why it would be useful to open the ground to the dome when the doors are closed if you can still turn the dome on anyway, so basically, Im still confused on this particular circuit, and finding documentation is not bearing fruit.