Mine came pre-installed so I can't help you... But I might have a suggestion
Just finished hooking up a SIDE VIEW camera... This was a low cost "Bullet" type camera (This is a simple camera that is something like a large bolt with wires coming out of one end and a lense in the other, Drill a hole about 1" or 1 1/4" (I don't know what size but I did have the proper drill) insert the camera, screw the nut down on the backside, hook it up and it works)
IT's right under the gas cap or filler door (in my case gas cap) so that when I select it,(It feeds video 2 on the back up mointor) and pull into a gas station... Well, all I have to do is center the pump on the screen and I'm where I want to be... 1st time, every time
I plan on a few more of these, but am looking for a lower cost supplier (this one was 27 dollars on E-bay, looking for 25 or less)