Back up camera not working.

So I just got a esky back up camera from Amazon. I have power going to the unit when I put the truck in reverse. However the radio won't display the camera. I have the rc a video cable ran all the way to the head unit, and it is plugged into the purple rca on the back of the radio. The radio "dual" brand is suppose to automaticly switch over when the camera has power.

The radio is used, got from my good friend. I've see It work. It just won't work for me.

what would you do first?

Problem fixed, had a short in the rca harness.

Good deal on getting it resolved!!