[peebee]

I've been trying to install a Road Top CarPlay unit into my 2010 320D. The device basically inserts itself between the head unit and the screen with a double-headed quadlock cable.

Was having issues with their wiring harness recognising the unit, and was about to give it up and return it as bad unit / incompatible with my E90/CIC system, when the worst happened - my screen and head unit both stopped working, and I began to get SOS comms errors on the display panel.

I've removed all of the additional items and am back to original equipment and cables, but still nothing on the screen. I've tried to reset the head unit by holding power and eject down, but nothing doing. The unit didn't have a CD inside before, but it took one and pulled it in when I started to insert it, so I know there is power going to the unit.

Any suggestions on next steps to try to diagnose?