Do you know if your horn OK ?    Sometimes we would peck on the horn with a hammer while someone held the horn button down.  Worked sometimes.
    The horn has voltage through it when the ing. switch is on.  You can take a test light or meter and see if you have current on both term. on  the horn. If you do ,find out which wire is the "hot" wire and then pull the ground wire off. Take jumper wire and put it on the horn then to a good ground. Bumper ? Are you still 6volt ?  If you have current to the horn but not out form  the horn,
 its bad

How about the wire behind the horn button that attaches to the horn ring ?  
    You can unscrew the wire and ground it to a good ground and if it works.
   Did you find the "push on "  connector at the bottom of the steering shaft housing right over the master cyl. and the wire coming out of the shaft jumping over to the rubber disc  ?   I have had a lot of trouble with the one on the disc before. You can loosen the bolt/nut on the disc where the connector is  and clean really good.

Anytime I start to work on VW horn, I go to link below, scroll down to the electrical section and click on "Horn Wiring Hell; How to survive it"  

http://www.thebugshop.org/bsfqindx.htm

Even if you already understand the circuit and have a wiring diagram, it's a good refresher.