Volkswagen camera retain
For the VW there is a camera retain cable which can be used with the 
Primary wiring harness.

Looking at the back of this plug below you will see two wires being for the 
camera
White is the video signal
Black is earth.

If your current aftermarket plug will have something connected to it for 
steering

This this cable cannot be used as it will already have a plug where this white 
plug needs to go
Removing the pins from this adapter cable and pushing them through is a really 
tough job with the tools and without is nearly impossible without the tools
Solution:
What you will need is to get from any Auto Electrcian, Bursons, Repco, 
Strathfield, Supercheap, Autobarn etc is 2 wire crimps like 

and a pair of pliers to close them
What you will get for this, to retain the cable is the open ended RCA.

The middle core (often red or yellow) will connect to where the white wire would 
be connected.
the outer / black will be connected to where the black wire would be connected.
The methodology is quite simple.   
As your cable is plugged in simply follow the cable to the car side of the 
connector and using the Scotchlock connectors join the wiring to the factory 
wires.