We bought the Rear Trailer Camera (84876819) for our 2020 Chevrolet Silverado. We want to make sure that the camera works prior to mounting it on the trailer. We connected the trailer to the truck, plugged in the camera, selected the Rear Trailer View on the display, but the view is black, there is no picture. We didn't calibrate it like it says in the instructions since it wasn't mounted. Do we need to do this or is there possibly something wrong with the camera or the connection to the truck?