2017 86 Trying to reinstall stock head unit
 

I had a Pioneer AVIC Z910DAB installed but am now selling the car and wanted to take it with me.

It was a bit of a mess behind the head unit, but fortunately the guy that installed the Pioneer seems to have used (at least mostly) adaptor plugs instead of cutting wires.

Everything is working with the original head unit except for the reversing camera. I can see on the diagnostics on the head unit that it's not receiving the signal that the car is in reverse, so I guess there's a reasonable chance the camera is plugged in and powered, but it's just missing that signal.

Sorry if this is a dupe. Had a look around and couldn't find the same thing anywhere.