I recently purchased an Audiovox overhead DVD system for my 2009 Tribeca and need to install it where the rear lamp is. I took out the factory rear lamp and it has Three wires: "Blue" Constant 12volts "Brown" Which has little power going through it until you open the door...Then the "Brown" wire is hot. The Third "Black" wire I'm assuming is ground. When I connect my overhead DVD player...the Instructions say how to connect this to a positive system or a negative system...Which one could it be? Has anyone installed an overhead DVD system and Know which one it is??