Wiring - vw-resource Wiring. Note: You will find excellent wiring diagrams for all makes, years and models of VWs at VW Wiring Diagrams. Also Note: Wire sizes on these and most other wiring diagrams are printed on the wire in mm 2 Americans who express wire sizes in gauges, see this Wire Size Conversion Table. This article includes the following subtopics: Engine Compartment Wiring How to Replace a 2003-2011 VW Touran Radio - Car Stereo FAQs Most car radios of the VW series are easy to upgrade, including the VW Touran radio. Check out the photo above. And, If you need a wiring harness adapter, connect the adapter to the original wiring harness first, then, to the new unit. Besides the connection of the wiring harness, you should install the antennas correctly, too.