added another horn to the van this last weekend, did the dual horn
relay the way the factory does it (in my '82, I did a homebrew
version with a little relay box behind grill, and separate power feed
etc).

I used  2 fiamm horns and the resulting noise is more like an old
Cadillac than a "Euro" toot :)

info here:

http://shufti.wordpress.com/2010/10/06/dual-horn-relay-and-wiring/

alistair