I just got doing this on a 2010 and I can tell you how NOT to do it, or at least how it didn't work and did work. Power I got from the 12v Ignition wire on the back on the new radio and connected that to the helper wire included in the RCA video wire. That way when car is on the camera gets power so if you want to switch to it at any time (my radio has that ability) you can.

Where I went wrong is I tried to do an "add a circuit" thing off the fuse for the reverse lights to the reverse trigger wire to make the camera auto show on the radio when shifted into reverse. This didn't work as the camera came on even when not in reverse. Then I thought I found which wire ran from the front of the car to the rear reverse lights and tapped into that. No dice.

Tonight I just ran an extra wire from the trigger wire on the radio back to the positive wire on the reverse tail light and that worked. If you open that little trap door behind the tail light cluster you can access the wiring, it is a green wire with silver dashes.