I had this problem. Take off the adapter. On the back you will see a copper ring. There is a post with a small wheel sticking up from the cancellation switch that rides on this ring . Make sure the ring is clean and not bent (use steel wool to clean it) and make sure when the adapter is tightened down, it contacts the wheel on the post. Take a piece of wire attached to the frame of the car and ground to the steering column nut . Horn should sound. Next step are the horns. Use a jumper wire from the positive terminal on the battery to the terminal on the horn. Touch it and the horn should sound. If the horns are ok, its highly likely the horn relay is bad. Its located just above the drivers side kick panel.
Here's a pic of the copper ring
View attachment 1715932780
Here's the wheel that rides on it.
View attachment 1715932781
