Thanks for the posts.
Firstly, it's not a wireless system. I have gone for another CCD wired system as per the one I fitted to my other Van.
It's a bit more complicated than running it to the reversing light. Primarily because it is not to actually supply a live for anything other than to tell my GPS that I am in reverse, so turn the sat nav route off for now, and show me whats going on behind us. In theory wiring to the reverse light would work, it is just that the wire is for the sat nav in the front of the Van as opposed to the Camera.
So the switch needs to go to a short wire (dead reckoning) on my GPS.
I "may" have found the switch on the top left of the gearbox (looking from the front), I don't know if anyone can confirm? I have to be honest, im thinking of changing the set up to a dash board switch rather than the reverse switch. This would be more beneficial if I wanted to see what is going on behind whilst travelling forwards (check on the bikes, etc).