How to replace horn and gasgauge relay?

Have you done any testing to see if horn will work? If you can get at horn wiring connector, take it loose, use jumper wires from battery for voltage and ground to horn connector. If it will honk, the horn itself is not the problem. Then there would be a problem with wiring circuit, somewhere, usually in the steering column. What about fuses?

Just to add, horn diagram. In diagram is horn fuse and horn relay. Green wire to horn is voltage. Black wire is ground. You need both.

Sorry, hit the wrong button. Here's diagram.