Need help with Pibus and RPi3B+

[TooEasyL2P]

Pibus suggest to use purple wire from Nav unit. But it's hard to get to it. So used reverse light plus cable and it didn't turned to black screen.
Measured pin on pibus itself to see if my connector is made ok and it shows voltage. Tho ~10.6 and not 12V. But maybe it doesn't really matter and it should trigger rear view?

I can try to connect to purple wire if that might work.