[dmjlambert]

Here is the approach I suggest

Disconnect the green wire at the horn.

Test the horn by connecting a jumper wire from the positive battery terminal to the horn. If it doesn't blare, then remove the horn and replace or fix it. I have heard of people spraying a bunch of WD40 in it and letting it soak, but I didn't have any luck with that fixing my horn. Some people take them apart and work on them, but I did not do that. I ended up replacing my horn. If the horn does work, then look further into the wiring.

Leave the horn disconnected and see if the horn button makes the horn relay click reliably. Check that the green wire leaving the relay gets power only when pressing the horn button. Disconnect the negative battery terminal at this point to get further into troubleshooting. Have a close look at the relay and its connector. This symptom sounds to me like a relay problem, or the connector on the relay has melted due to bad and rusty connections inside the connector.

Remove the horn button, the metal cup and plastic retainer and convex spring under the horn button and looked to see if it looks OK and if there is any damage. The horn honking on it's own kind of sounds like foreign material of some sort shorting out the horn button hardware inside the steering wheel.

Inspect the wiring thoroughly for melted wires or connectors. inside the cab there is the connector that goes through the firewall that you can access by removing the 2 screws to the fuse box and give it a good look. There is a crimped junction of the 12 gauge red wire in the wiring harness, and a plug on the horn relay on the firewall. The 12 gauge green wire powers the horn. There is a curved connector to the wiring that goes up in the steering column.

In the engine compartment, disconnect the wiring connector at the firewall, separate the connector into the 2 halves (engine harness and front harness) and pull the wiring and connector to the front driver headlight area through the inside of the fender and get it out in the open so you can inspect it. The wiring bundle that runs through the fender was a meal for rats on my truck, so I had to repair all those wires and re-wrap them. If you need to re-wrap, it is non-adhesive black vinyl tape you would look for to make it very neat and I found mine on Amazon. Continue to inspect the wiring all the way from the firewall connector to the battery junction block, and make sure you have a short section (about 6 to 9 inches) of 16 gauge fusible link wire at the junction block to the battery terminal. Fusible link wire has a soft non-flammable insulation and usually is black or grey. The wire may be fried inside it, so try stretching it by tugging on it with your fingers to see if it is good and solid.