Mazda3 generic reverse camera installation

[scubaal]

OK. Son has a MAzda3 BM 2014.
We just replaced the existing infotainment with generic android carplay unit.
All working just fine.
This car did NOT have a mazda OEM reverse camera.
We have a generic reversing camera to install. On other vehicles I have tapped the power for the camera into the back of the reversing light - and used it as the trigger wire for the head.
But in the Mazda3 the reversing lights are controlled by PCM/RBCM signals so I have been told this is a no go? Is that correct?
How should we wire in the reversing camera? I know there are a million posts on this stuff but it just seems more confusing the more I read.
To be clear - there is NO OEM camera or OEM head.
Its a cheapy camera to an Android 15 head that has the standard 'RCA Video + trigger' connection at the head end.

 

[scubaal]

Seems the 12v to the reversing lamps comes from RBCM pin 4S. Some posts are saying 'connect to RCBM post 4S' - but essentially this is the same as connecting to the 12v wire in the back of the reversing light? So any problems doing this?

 

[theblooms]

All the radio needs to trigger is a 12V signal. Just tap at the reverse bulb using the red wire that every reverse camera has built-in to the RCA video signal cable.