If the RCA jack is plugged in and everything else works on the radio, you may have a fried connector at the rear where the camera plugs into the harness.
My class C has a curved panel at the rear ceiling... it's just stapled in place. If yours has one, carefully pry the panel loose. The camera cable comes in through a hole right behind the upper tail light. The camera cable plugs in to a harness, (RCA) which carries the signal to the radio in front.
Mine had shorted and was replaced under warranty. If the camera is toast, they're available here...
https://www.123securityproducts.com/...RoCJKoQAvD_BwE