[markeb01]

I believe you already verified the horn button is operating correctly, but one possibility with some of the early Grant/Superior/Covico style adapters - there is a small channel on the top surface of the main aluminum hub portion of the adapter where the horn wire is suppose to rest under the bell. It's very easy for the wire to pop out of the channel and get pinched between the hub and the bell, resulting in a runaway horn. Just something else to check for the next guy having a similar problem.