Some of the wires have different thicknesses. Do I have to get wires that match the exact thickness?
I used 24 gauge 0.2mm wire from maplins, with 3.5mm heat shrink to cover the soldered joints.
This is thicker than most of the wires, but good enough for the thicker wires.
Wire:
http://www.maplin.co.uk/p/maplin-equipment-wire-24-02mm-black-10m-kr31jThat link is for 10m, you wont need that much, they sell smaller quantities in store.
The next thickness up from that is 32-0.2 if you want to be extra safe. It's all to do with the amps / current that the wire can withstand.
Heat shrink:
http://www.maplin.co.uk/p/35mm-heat-shrinkable-sleeving-1m-bf88vIf you want it to be 100% matching you'll need to buy individual repair wires from VW, but I don't think its needed.
Once repaired, I wrapped the bunch of wires in insulating tape before covered back over with the rubber sheath.
My brothers was done nearly 2 years ago and it's still fine.
I'm up in Lancashire, if you're near, I could help you, I have the wire.
Jas