Got mine working, except for the rear fog. These threads helped a lot.
Using the ECS harnesses, I had a couple difficulties - the harnesses weren't built right, even for a Jetta, so I was doing some mods on the "purple clip" side that I didn't think I would need to do. I think I totaled the purple clip on one, but it still works OK.
The second difficulty I had with the harness was that they should be "handed"; the left harness is different from the right harness. I built two "lefts" and it was obvious when I was plugging in the right one that I had goofed; the wires were all shifted one position.
After doing the coding from speedbump, they worked fine for a day. Then today, I got a "bulb out" diagnostic, along with an MFD message about the right brake light. I could observe the right parking light was either not on or very weak. Thinking it had to be a coding error (or DTC clear error), I of course cleared my codes a couple times. Finally I pulled apart the right taillight again and discovered I had pinched a wire under the stud, shorting it to ground intermittently. Sometimes a fault is truly a fault.... And of course *this time* I dropped the damn nut down the fender 15 minutes with a flashlight, dental mirror and magnetic pickup tool saved that one.
As for the rear fog light: I connected the trigger wire to the switch, and I pulled off the lower dash cover to access the ECU. I then moved the seat and tried playing "twister" to get my large middle-aged self under there a few times before I decided I would be royally pissed if I slipped a disc or something trying to do this. Either I need to pull the seat completely out, hire a twenty-something to do this, or settle for no rear fog light (those grapes are probably sour anyway....)