I had a backup camera installed in my D3, it seems to be working correctly (when put in reverse it will automatically come on) but lets say if i go to the nav screen and want to view the traffic behind me with the cam it shows just a black screen. Is this because it is connected to the reverse wire and therefore only has power when in reverse?

Also if i go to the status screen it says "Back Signal - High" when in reverse and "Back Signal - Low" when in any other gear. Is this the correct reading?

They probably used the reverse lights as the power source for the camera. They need to connect it to contstant power for you to use it while not in reverse

Actually, they need an ignition switched ACC power source... so the camera doesn't stay on when you turn off the car.