in my case, the factory TV tuner takes over the screen, even if the Nav has not fully booted up - once i throw the gear in R, the screen flips into the reverse image... since i used a wireless transmitter / receiver, i get wireless interference from the headlight system and from other external sources (plenty of those sources around Pentagon!!!)... i will run an actual wire someday - if the interference gets under my skin - i am ok for the time being...
next time i dig into TV setup when I wil l run the AV wires to the factory locations in the rear center console... sometime in the summer...