There are many causes that can lead to a broken car horn including a problem in the button or switch, a problem elsewhere in the electrical system or wiring connections, a problem with the horn relay or a burned-out fuse. When diagnosing the problem, first check the fuse box for a burned-out fuse or faulty wiring, and if the problem remains, check the horn button, the horn relay and finally the horn wiring.
The most common issue with a faulty car horn is the horn fuse. The horn fuse is located inside the fuse box, under the hood of the vehicle. If the fuse is burned out, replace it and test the horn to see if it now works. If the horn is still broken, check the wiring inside the fuse box, and make sure there are no problems with the connections.
If both the fuse and the wiring in the fuse box are OK, check the horn button. Remove the steering wheel cover, and look for any debris that is preventing the button from being fully depressed. Remove any debris, and try the horn again.
If the problem remains, check the horn relay. Have an assistant operate the horn button at the steering wheel while you test for voltage at the relay circuit using a voltmeter. If the relay is not working properly, replace it. While checking the horn relay, also make sure that all of the horn wire connections are OK. If there is any corrosion or disconnected wires, fix them and test the horn again.