On the inboard side of the column is a long connector with about 10 wires in it. Using a jumper, and a paperclip to make a connection, short the black wire to a good ground. Horn should sound. Or the relay should click. Relay is adjacent to the park brake release handle.
My vote is for a broken wire retainer behind the horn button. Very common. If the test above sounds the horn, remove the horn button. The bottom two pics in this post show the horn button contacts, and the little tabs that get broken.