Today, I accomplished the rear foglight mod on my 2006 TDI. Everything I wrote originally still applies with the exception of the rear foglight assembly which is different from the 98-05 assembly and the Turbo S assembly.
There are a couple of suppliers for the assembly. I purchased mine from ECS Tuning (
www.ecstuning.com). Look under 2.5l beetle and you will find it. This applies to the 2.5 and 1.9 TDI. You still need the euro switch and a wire to run from the switch to the back of the car. ECS has a wire kit that works well. It costs $13.95 but is worth it. The bulb that comes with it won't work but that's OK. The assembly comes with the socket and the bulb. Your reverse socket/bulb will work just fine.
The other supplier is
www.oempl.us. The sell the assembly and a "trigger wire". My guess is the "trigger wire" is either a long wire to run from the front to the back or it is the little short wire that is discussed above.
A couple of notes.
It would really help to have the VW terminal release tool (
http://forums.tdiclub.com/showthread.php?t=228942). This tool will help you push out the blue/black wire out of the existing plug at the rear assembly. This is really handy and will make the task much easier. On that same page is a link to a description of how to use the tool. You need to study that. I was lucky and got the tech at the dealership to push it out for me. There are 2 pins in the plug and are marked #1 and #2. #1 should be the blue/black wire - push that pin out. Run your wire from the switch to the back as discussed above.
There is a rubber plug in the spare tire well just behind and to the left of the license plate. Slice a hole in the rubber grommet and feed the wire through to the outside. You will be right beside the assembly. Plug in the wire into the now empty slot. Plug everything in and put in the new assembly and test. You should be good to go.
Here's a picture of mine with the light illuminated.