I did this install in about a half hour.  It was simple, however, try at your own risk.......

 

Parts needed to install the "factory" rear fog lamp on the B5 Passat :

- Euro headlamp switch (avail. from Neuspeed and many others about 90 bucks)

- Enough wire for routing from headlamp switch to left rear taillamp housing

- Two butt connectors or soldering iron and electrical tape

- VW wiring repair piece  Part # 000979133 or 000979126  yellow color (about 3 bucks)

 

 

Directions  -  Please read completely before starting: 

1 - Remove the headlamp switch by pushing in and turning to the right, then pull out. You may also remove the Daytime running light relay to disable the DRL feature             at this time.

2 - Take the yellow wire that you purchased at VW and cut it in half.  You will need the factory crimped ends, one at the headlamp switch and one at the taillamp.

3 - Take your long piece of wire (I used 14ga yellow) and butt connect (or solder/tape) the long wire to one of the yellow VW pieces.  

4 - Look at the rear of the Euro headlamp switch and fing the terminal labeled NSL.

5 - Carefully install the VW wire end into the headlamp switch wire harness where it will contact the NSL terminal when you plug in the harness / switch. (it just plugs in)

6 - Plug in the harness /switch and install the switch in dash.

7 - You will now find that the new Euro switch has more switch positions ( off, parking, headlamp, fog)

8 - The new switch allows you to pull out one click to activate the front fog lamps and two clicks for the rear fog.  See below.

9 - You are now able to run the fogs with the switch in the parking lamp position.

10- Route the long wire along the sill panels, out of sight, to the drivers side tail lamp housing.  Remove the bulb holder from the taillamp.  

11- Attach the other VW wire end piece to the tail lamp side of the long wire using butt connector.

12- VW has thoughtfully placed a rear fog bulb socket at the existing bulb holder (lower left as you are looking at the bulbs)   Install a standard 1156 clear bulb.

13- Plug in the VW wire end to the factory connector at the drivers side taillamp wiring.(examine the connector and you will see a blank spot where the wire should go.

14- Use pliers, a utility knife, or a large drill bit to enlarge the existing socket in the tail lamp housing so the 1156 bulb head can fit inside. 

15- Reattach the wire connector to the bulb holder and install in the taillamp lens.

 

You should now have a functioning rear fog lamp with the switch pulled out to the second click position.  

 

NOTE:  There is no indicator lamp for the rear fog on the switch or dash.  I found that there is an indicator lamp icon, for the rear fog, inside of the Tachometer face but I haven't yet figured out how to make it work.  When I do, I will pass the into on to you.

 

Also, you may be able to do the same thing on the passenger side however , in Germany, the rear fog is on the drivers side only.    

 

Good luck!