Have you tried hooking up a test light and having someone beep the horn? If the light lights up, the wiring is good and the horn is bad. The other test is to run two test leads from the horn direct to the battery. Either test should tell you if the horn or the chassis wiring is defective. If the horn is bad, JCWhitney sells all kinds and sizes of replacement horns and I have had very good luck with their mail delivery service.