Found a little more info from autopumpkin.com. Here is a basic layout of one camera harness like I think I have ordered. It also shows power from the reverse light 12V but on our BMW's this causes issues. So with a relay it should work but still, this only has camera powered up when reverse is engaged. I want the camera powered up always when key is on for recording purposes, not for viewing on monitor.
Another wiring schematic for some different camera systems that have a dedicated analog reverse light signal sent to the HU if you don't have the help of IBus messages to indicate the reverse signal.
And finally, the message at the bottom:
BE NOTED:
If your headunit is using the CAN BUS decoder box to control the reverse signal, then the reverse detective wire should be already connect between the CAN BUS box and the headunit, then you no need to care about this wire, just connect the RCA jacket to the camera input port from the radio.