200 horn button problem

[Lee Levitt <wheelman@pipeline.com>]

Folks, 
 
I noticed that the horn button on our 1990 200 seems to work on three of
four corners. Feels like there is an electrical contact at each corner. 
 
Naturally, it's the fourth corner that we want to use (top right). Of
course, on the 200, the horn button is actually a large pad that covers
most of the center of the steering wheel, and behind this pad is a very
expensive explosive device that only deploys in a crash or during minor
electrical disturbances. 
 
Anyone ever fool around with a horn button/pad on an airbag equipped car?
Any pointers other than get a pull chain and a truck airhorn? 
 
Thanks in advance, 
 
Lee Levitt 
 
wheelman@pipeline.com 
1990 Audi 200 63K 
1988 Volvo 745T 108K