I recently had an interesting problem with my Vanagon, the horn would go
off when I used the turn signals.  Although this was slightly amusing,
it is a very bad thing when you have Hella air horns.  I removed the
steering wheel and found the problem to be with the turn signal/wiper
switch assembly.  There are two brass screws at the top of the assembly
that had completely backed out and were letting the assembly move around
and short the horn to ground.

dave
www.251.org