I know you are specifically looking for a wired backup camera, but I can't help but throw this out there.....
You can get a wireless backup camera and monitor for ~$150. Since you probably want to mount the camera up high, you likely (right??) have rear upper running lights. You can tap off power from those and mount the camera right under the running lights. Then, to "turn on the camera" from up in the cab, all you need to do is have your running lights on. (Personally, I always drive with the lights on just for extra safety/visibility).
Time to complete the job...less than 1 hour.
-Chris
