I have a backup camera to set up, but checking which wires go to which light isn't easy since the bulbs are mounted onto a circuit board instead of visually being able to see where the wires go. Upon a little research I see that other models use the yellow wire for the reverse bulb. I imagine that the black one is ground but I would like to make sure before I mess with the wiring.
Your best bet is to back probe the yellow wire to see if it's the one you need. I have used a needle attached to an alligator clip on a wire as my probe mechanism. Works pretty slick without damaging anything. Just set the emergency brake before you do anything.