I am attempting to hook up this USB. I'm not sure it is working. Going by the wiring diagram. It shows a 12V supply has to be used at the panel. I will assume the "track" wire coming in/out of the left rear port is the wire going back to the Power Pro box. The left front port to the Power Cab and the right front to the USB. Do I need to get a 12V wall wart to power the panel to get the USB to turn on ?