The attached is a pic of my radio with the upper part of the dash removed. In the upper left corner of the opening, about 11 o'clock, there is a black box with a white label. If you blow up the picture you can see the camera wires going in and there is one that comes out and plugs into the video jack on the back of the radio.
If you have the Jensen 212 radio I believe that is a single input radio as well (not positive) and that would require you have some kind of controller somewhere.
I found mine when I removed the top part of the dash looking for loose wires. My radio will intermittently loose power.