Red Wire - Connect to the Reversing light positive feed.

Black Wire - Connect to a negative power supply (Ground/Car Body).
I am trying to install parking assist system on my car but I don't know where to connect the black wire:confused:
so what is Ground/car body?
thanks in advance

connect it to a metal piece that is connected to the frame of the car, where is the wire at?

Oh nevermind, I found it. I was trying to install backing up sensors on my Continental. The positive and the negative were in the same spot.