EtoileBrilliant

Putting in a rear view camera in 2011 W204 Wagon. I need to connect positive to reverse wire and negative to ground. I have done this successfully on my Smart 451 so I have half an idea what I'm doing ;-)

Question 1: does anyone know the colour of the reverse wire in the tailgate and is there an earthing point in the tailgate?
Question 2: my preference is to hide the wiring through the flooring (rather than play poker with the side airbags), does anyóne know how to remove the panel to access the D-Pillar wiring loom?

Google has been of some help but information on the W204 estate is thin on the ground.

Many thanks in advance