Just had the same problem with my Holiday Rambler Admiral 2006. It turned out to be the connection at the rear camera to the cable running to the monitor. Cleaned it and applied some contact seal/lubricant and all is good. The camera had about a two foot lead on it before the threaded connection, it was inside the rear wall and I just had to pull it out to expose it. You can remove the camera and plug it into the back of the monitor to test it.
2006 Holiday Rambler Admiral
2013 Jeep Wrangler 4/Door