By the way dont just replace the relay. Heres how you test the horn, relay, fuse and all the wiring all in one step.
Okay we know where the horn is located right? You simply unplug the horn, stick a 12V test light into the connector, ground the other side and have someone hit the horn......does the test light shine, if so fuse, relay, and wiring is good, so what isnt good the horn itself.
See how simple that is, dont start " well going to toss a relay at it", did you even check the connections, do they have corrosion, is there a damaged wire someplace?