Here is a fast way to determine if the horn is bad or the wiring is the problem. If your wiring appears orig. , take a test light and with the Ing, switch on, test for power at both terminals on the horn. If you only have power on 1 terminal , you can bet on a bad horn. These horns are suppose to have power out of both horn term. with the switch on. The horn works when you ground the ground wire with the horn button. If you have power out of both term. and can determind which wire is ground after all these years, you can slip another wire on the horn and ground it to see if the horn works at all. If the horn "grunts" or tries to honk , still could be a bad horn but does tell you that the problem could be at the rubber disc at the steering sector ( a little jumper wire) or at the bottom of the steering column (over the master cly) on some models, contacts behind the steering wheel and if you have a really old or euro car ,there is a little tube on the steering column about where your right knee is that has brush holder that can cause a problem.
If you have no power at the horn at all, chase the 1 and only wire straight back to the fuse panel.
God only knows what has been done with the wiring after all these years ,so good luck. :lol: