With Rearview systems there is NO WAY to accurately diagnosis an intermittent type problem. All you can do is a best guess. IF you have side view camera's(probably NOT on a 2002 Newmar), when the rear camera goes out you check for side and if you have display you know it is either the camera or the cable. There are no tests other than replacing a part. MOST times it is the Rear camera, since it is exposed to the elements. What brand system? ADTH? You also make sure the camera cable plug in at the rear of the monitor is tight and secure. Sometimes they are loose and cause intermittent display. Doug