My van has six stock horns supplementing the original stock horn. I
stole the idea from Haywood-Sullivan's "Sunny":

http://www.haywood-sullivan.com/vanagon/vanagon2_detail.html
http://www.haywood-sullivan.com/vanagon/horns_detail.html
http://www.haywood-sullivan.com/vanagon/dual_horns_wiring_diagram.gif

It works great, stock sound just much LOUDER. You can still illicit a
soft beep by tapping the horn gently.

Chris

On 11/6/06, Kevin Mulligan <mulligan_kevin@yahoo.com> wrote:
> I got one of these Hella double horns and have had good results:
>
> <<http://www.rallylights.com/hella/supertone_horn.asp>>
>
> With careful fitting, I was able to leave the existing horn unchanged and
> wire the existing horn ground (coming off the steering wheel) to a switch
> that lets me change between the existing horn and the Hella horn. The
> Hella is very loud and works well on the highway.
>
> - Kevin
>