Just finished sorting the electrics on our 2009 320GT. Apart from swapping the fog light and reverse light, the main job was installing a leisure battery to power the motor movers and provide off grid electric. For some reason, Eriba give priority to the 12v towcar supply which automaticlly cuts off the mains supply when 12v is energised. This means that even if you are hooked up to mains, you could still be draining your battery if it's still connected. I dare say you could fit an ac relay somewhere to cut off the battery supply but I have followed a simpler route. I have taken a wire from the "towcar input" (bottom terminal on the control box) and fed that into the "common" terminal of an "on-off-on" switch. The two "switch" terminals are connected to the towcar feed (black wire) and the leisure battery (via a fuse!) Respectively. This way I can manually select between towcar, leisure or neither with the switch. For good measure, I have included a led in the circuit so there is no doubt when one or other of the 12v supplies is live.