There are 2 different kinds of camera systems:
1. A Back-up camera works when vehicle is placed in reverse.
2. An Observation camera is the one that allows you to see who is behind you while you are driving down the road.
During our PDI, we were told that we had to have the truck's running lights on in order for our wireless observation camera to come on, and the display needed about 5 seconds to power on once plugged in....and were given the box containing the display unit with a mount.
I use it when traffic is heavy and like it. I did have to climb up and adjust the look-down angle to get a wider/further view of what was behind me.