Reverse Camera power??

[UPGrayd]

So, with a little bit of time off work, and what little time I have without the 18 month old screaming for my attention, I have used this weekend to put an xtrons head unit and reverse camera in the wifes X5. No dramas with the head unit and extension loom to the back (apart from the obvious PITA of running it through the car)...Didnt even have to wire anything extra up to get the steering wheel controls working like i've had to on other cars...brilliant..couldn't be easier!

Hell the Xtrons even knows when the car is in reverse and flicks over to the cam input already! Thats going to make my job even easier with the cam as I no longer have to worry about the signal wire to the head unit! wonderful!

So I go to wire the cam up the same as I have with literally every other cam I have installed in a car...tap power and ground straight from the wires from one of the reverse lights and I'm good to go!....except.....not......Camera is flickering on and off like crazy....Ok so im guessing the big girl is also sending some sort of bus data through that for the bulb monitoring systems?

No biggie, I'll pull power directly from the battery in that case, its right there in the back anyway, and tap the signal wire for the cam to power up from the +ve on the reverse light I was pulling power from before...great..everything works as it should.....Until I turn off the car, pack up all my tools, put all the trim back on, close the tailgate and notice the reverse light I pulled signal from is on......just the one.....what the actual F!$@?! I open the tailgate, pull the service panel out of the lower half and back probe the plug for the reverse light and see 8.9v? Having had enough of the car for the day, I cut the 12v to the cam, Reverse light goes off, and I walk away from it for the day.

Whats going on? Is there something I have forgotten between now and when I did my last reverse cam?