Reverse signal feed for camera

So a few years ago I changed the Sony head unit for a  cheap chinese Android unit. I never fully wired it in because the person who owned the car before me mashed up the cables. I think they thought the overhead screen cable was for the reversing camera and chopped it to pieces trying to work it. The screen lasted a few weeks before giving up and it was returned at my cost. Note - dont buy cheap chinese android head units.

Anyway the old Sony unit went in with a new connection for the rear camera after I found the wire tucked away and got an adaptor, however it was just turned on with the head unit, never the reverse. I did find a 4 pin plug that was lose that had a 12v ign feed, an earth, a cable that was 12v when I use reverse and a 12v for the parking break signal.

I now have a new quality android unit and got a new cable for it with a canbus, however there are 2 brown leads, one coming from the head unit loom saying reverse, one coming from the canbus saying back.

I have read on the Teyes website (who supplied the canbus), not to connect the reverse lead if its controlled by the canbus because it can cause damage.

Anyone fitted an android unit with a canbus? Is the 12v lead needed and if so, where do I connect it to. The canbus lead or the wiring loom? Or do I join "back" lead from the canbus to the "reverse" lead on the head unit loom?

On a side note. Is there a way of tapping into the original microphone by the dome light?