The parking sensors take power from the reversing light wires. Any power needed will be taken through here when you put it into reverse.
I'm after fitting some of these myself, but not with the wireless display, rather the speaker.
Am I safe to assume that the speaker is powered by the control box that it plugs into, or is extra juice required from another source?
Set in question: eBay
And StanH, if you can get two friends, you can do what I did to check: I dropped the back seats, me and my brother climbed in and held the sensors where they needed to go and my dad walked in front to check the positioning was correct. Only then did we drill.
Also noticed you have a 2006 Ghia like GSM and me. We both found our car's differed from Preee's car in the guide. Would you mind posting if yours does to please? Would be interesting to find out why this occurs.
Any more advice needed, just post :-).