Just pull off the connector on the back of the hitch plug. You will see a large red wire going into the connector. That wire is hot all the time...

 

I think he wants a wire that is NOT hot all of the time.
I haven't put a backup camera in mine yet, but i did in my wife's nissan, and i used the reverse light wire. it's only hot when you are in reverse, so you won't be able to use it when you are driving forward, but i had no need for that anyway. I like the setup that way, so the camera is only powered when in reverse. who knows how long these cameras will last if powered on all of the time, so i figure less is better!

 

One option would be to power the camera, or at least to trigger it to turn on, is to use the running light. That way, when you are trying to line up a trailer, it won't be limited to just reverse. I would still want a way to turn it off in the cab when I don't want it on.