The wiring block that goes to the rear lamp cluster , put the ignition on and make sure it's in reverse and ensure no side lights , brake lights etc are on.
Get a power probe and probe each connector terminal to see which one is the positive feed (red light on probe) . When you find it take note of which wire that it was and leaving the ignition on take the gear selector out of reverse and re probe the same wire , it should now be a negative (green light on probe)
I'm now sorted the reverse wire is brown if anybody else wishes to have a go installing a camera or sensors.
It was pot luck for me looked at the cluster wires on both sides and saw only 1 brown wire so thought why not try it - this was after going to local dealer this morning who told me that he would have to hook it up to find out, cost £60, after asking him why he needed to hook it up to tell me the colour of a wire he said it was the only way to find out.
I suggested to him that i'm sure one of his fellow mechanics could probably tell me of the top of his head since they had a big sign offering after sales extras such as front and rear sensors for ££££sss.
After the confused look from him I then told him thank you and goodbye as he would not be seeing me in 6 months for my full service and check before the warranty expires and first MOT. He looked and I looked :lol:
I have just done this job, not fitting a camera but reversing sensors, on my 2012 107. After some testing I found the Green/Brown wire position 4 in the block and the Red wire position 2 were the correct combination.
I know that a lot of people mount these within the black bumper trim however I went for just above spraying base and clear coat.
The operation is good, as too is the colour match.