If you cut off the plug before the split to the yellow and red connector, there is a shield (bare strands), yellow (video+ connects to the first blue wire) and Red (12v positive) to power the relay to open the second blue wire. 12v positive power is supplied from the back up light at the rear...
For those interested ,I made some 3D printable 4x6 adapters to put 5x7 speakers in the rear deck. (BTW, they are screw with no mods required so even if you lease you can undo this addition and put back to stock at the end of your lease.)
https://www.thingiverse.com/thing:2938980
To adapt...
I wired my backup camera to the user "padavos" on page 13, (thank you very much) and I noticed that my camera worked without connecting "video-" to the purple wire. I checked the resistance of the purple wire and it is not 0 ohms to ground or "ground" and so I did not connect it. Maybe this...