To add a reverse camera to my VW head unit without paying daft VW prices I used this loom:
Adapter harness to add a reverse camera to an original Volkswagen radio screen. This harness has a built in interface to give ignition power and a reverse feed to the camera. Note, camera input function needs to be CODED to the car by a VW dealer or a specialist engineer with VCDS.
incartec.co.uk
With this camera:
The results are great, plays nicely with my parking sensors, the music quietens when reversing as before, and the picture quality in both day and night is as good as you’re ever going to get on these Disco screens.