First things first.
Find the horn wire where it comes out of the steering mast and check to make sure that it is not grounded out to the steering mast from deteriorated wire insulation. Use an ohmmeter.
If all is fine, attach the ohmmeter at the horn wire and a good ground, then push on the horn plate to see if it reads on the ohmmeter as next to zero resistance.
I don't know how your dash button is wired.
The original horn button provides the ground to a relay, which then energizes the positive wire on the snail horn. The snail horn bracket grounds to where it is attached to sheet metal.
