I have a 2011 Silverado with the Bose package and the Nav HU. I would like to be able to turn on the stock backup camera while in drive. It would be useful for when I'm towing my boat. I have found the wire that sends power to the camera and have wired it to an accessory wire to come on with the truck. I having trouble figuring out how to make the HU swap the the camera mode/input. I tested all the wires going into the back of the HU for any change in voltage from park to reverse but found none. I'm kinda leaning toward it being some kind of signal rather than a measurable voltage. Any ideas? All help is greatly appreciated.