As Peter says it is most likely the horn wire, but I would first remove the horn button to include the S-wire that activates the horn to see if it could be the S wire. Take the car for a drive to see if the horn blows without horn button / S wire. If it still blows then it is most likely the wire down through he column, and if not then it may be the S-wire prongs are making intermittent contact.
When i replaced the Mast Jacket Bushing / Horn wire, rubber button piece, and S wire for my horn back in the early 1980s the first place I took my car was to the fall Hershey car show, which is 30 miles from where i live. Every time I made a hard turn on the show field my horn blew. Turned out the prongs on the end of the S wire were just a bit to long. I ground a few thousands off and have not had a problem since except the button rubber is now getting a bit stiff and the horn is getting hard to blow. I guess it is time to buy a new rubber part again.