The last time I replaced taillight/brake/backup bulbs in our '05 wagon, I noticed that the spot where I assume the rear fog light would go was blocked by a plastic shield -- the shield was actually part of the assembly, although maybe it can be removed with a keyhole saw to do the five-light mod. (Don't know if the '03 wagon taillight is exactly the same as our '05.)
Getting the bulb holder out was more of a task than I expected. I actually had to remove the entire taillight assembly -- had to pull the entire lens off the back of the car, after removing the three securing nuts on the inside, which are not easy to get to.
To do this, I needed a small socket handle, two extenders (six-inch and two-inch), an eight-millimeter deep socket and an eight-millimeter swiveling box end ratchet wrench. A friend actually removed the nuts the first time, and had to be extremely careful not to drop them down inside the well.
The removal is documented on Page 94-16 of my Bentley manual. Wish I had some pictures to post, but I haven't gotten around to it yet. I'll be interested to know if you actually manage the five-light mod.
Oh! The A4 Golfs bulbs are much easier to replace.
I think I remember that plastic over over the bulb hole in the reflector/lens assembly now! I think it came out just by pushing and pulling: just like if you've ever built a miniature plastic model car / boat /airplane, the plastic pieces come apart by twisting to break the small connecting pieces, then you can just file off the edges if they did not come apart cleanly enough.
These are pictures of the RIGHT tail light assembly.
Don't mind the darker splice on the green wire. That's for the trailer wiring.
The light arrangement on the wagons is pretty silly.
Top: running and BRAKE
Bottom: reverse (inner), turn (outer)
With the headlights on, the brake light doesn’t jump out at you. This is why I removed the running light (2nd one down) and added a brake light to the blank slot.
You'll need to take a hot knife or dremel to the housing if you want to use the 3rd slot because it's blank . I enlarged the 2nd slot to run an 1156 base bulb.
Be sure to test fit the assembly before screwing the housing/lens back to the car.
Pull upward and inboard on the housing while tightening the hardware. The turn signal center conductor may short against the sheet metal. Note the tape for troubleshooting.
The 3rd bulb on this assembly is reversed polarity. The center conductor is grounded and the outer conductor is the positive. If you run LED bulbs you may have to re-wire them.
The left side brake also uses a red/black wire.
No problemo. I was working on this yesterday after getting behind a wagon in traffic and realizing how little brake light contrast there is with the lights on. Now I know why the rear bumper sticks out so much.
You’ll really like the effect with that small bulb (2nd one down) removed. The resulting dark gap between the top bulb and the extra brake light catches the eye.
I did notice the 3rd lens slot is pretty short. A high-wattage incandescent bulb might heat up the top and bottom plates.