Update!
I used these steps posted by a member on the Vortex to achieve what I was attempting to do. See below:
Wiring
The European wiring harness has 4 wires (Turn, Brake, Parking, Return/Common) running from the central electronics control module (J519) to each of the taillights. The US wiring harness only has 3 wires (Turn, Brake, Return/Common). To get the LED's (or Euro R32 lights) to function properly, you need to provide a signal to the 4th pin. There are two ways to do this. One may result in a "bulb out" message on the MFD and the other (adding a 4th wire) does not. Both cover both below:
The pin configurations at the taillights are:
Stock Left (Driver's side)
1. Not used
2. Black/white (turn signal)
3. Black/red (brake light)
4. Brown (common/return)
Stock Right (Passenger side)
1. Brown (common/return)
2. Black/purple (brake light)
3. Black/green (turn signal)
4. Not used
The wires need to be moved in the connector using the method described in the Jetta LED DIY instructions (Thanks to those who wrote the Jetta DIY  )
LED Left (Driver's side)
1. Black/white (turn signal)
2. Black/red (brake light)
3. New Wire (Parking light)
4. Brown (common/return)
LED Right (Passenger side)
1. Brown (common/return)
2. New Wire (Parking light)
3. Black/purple (brake light)
4. Black/green (turn signal)
The new wire should be
VW part 000 979 141 (I have been told that wire
000 979 151 works better, but I have not verified this). This VW wire has a connector on each end. This allows you to cut the wire in half to have a pigtail for each side.
The two new wires need a signal to activate the parking lights. The first choice is to splice wires 2 and 3 together as shown in the R32 taillight DIY. The lights will work just fine if you do this (after VAG-Com changes), but you will have an error message in the MFD that you won't be able to clear (this did not occur when setting up my Euro R32 tails using the splicing method).
The second method is to run two new wires, one to each side, from the Central Electronics Controller (J519) to the taillights. To do this, you need access to the central electronics controller. I found the Jetta rear foglight DIY to have better instructions than my Bentley manual. To connect the wires to the central electronics controller, you will need
VW part 000 979 025. This wire works just like the one for the taillights. Cut this wire in half and install the wire for the left (Driver's) side to connector C, terminal 10. Install the wire for the right (passenger's) side to connector B, terminal 9. You must then run wires from these pigtails to the pigtails in the back. One suggestion for routing the wires is to read the GTI sub DIY for routing ideas.The instructions in the Bentley manual for removing the trim may serve as a better alternative.
Here's a picture of the central electronics control module:
VAG-Com Instructions
Once you have connected wires to all four pins and reinstalled the connectors into the taillight housing you are ready to recode your central electronics module. This coding appears all over the Jetta LED threads, so I don't know who to credit for this information. Using a VAG-Com, you need to make the following changes to the Central Electronics Module (09).
**Note: These changes only apply to those installing OEM LED tail lights
Change Bytes 9 through 13 from
14 00 00 00 14 to
0A 00 00 0F 00
Change Byte 18 by unchecking the cold diagnostic bits 1, 3 and 5
Change Byte 19 by unchecking the cold diagnostics bits 2 and 3
Euro R32 Tail Lights running the 4th wire:
Change Bytes 9 through 13 from
14 00 00 00 14 to
0A 00 00 0A 00
Hopefully this helps, but as always YMMV.