Originally I wanted to get the signal from somewhere up front for the HU as that would make the most sense. However due to time we we had in the garage, we didn't come up with a great option for doing so since the tail wires run outside the vehicle until they reach the rear.

We ended up running a positive signal wire along the same route the video cable runs (so along the driver side floor, behind the trim). This was the quickest and easiest for us since we already had that side of the car pulled apart. So both the camera and the HU pull power/signal from the same point in the rear.

If you were going to hook it in up front you'll have to either go through the floor or through the firewall but I don't have a definite answer for you on that one as for where would be best for it