Hi Gableguy,

I sourced a few harnesses and dash kits on Crutchfield (who iirc unfortunately don't ship to Au, or the shipping was cost prohibitive) and found and ordered them on amazon.

I'm not sure if your Passat will have the battery drain issue if you install a 3rd party head unit like a Pioneer, but here is the harness that I got to prevent that.

Here's the recommended harness for steering wheel controls for my car. I ended up getting one from No Limit here in South Melbourne who finished off the install and also put in my reverse camera which just plugged and played with the Pioneer.

You may need a different harness to that though in order to enable integration with all the parking sensors, get the engine data etc to the graphical display. Perhaps something like this Vw Data & Display Retention Interface.

Have a look at Crutchfield's site, as well as youtube to see what others may have used in their installation. Good luck with it!