I have a 1975 Scout II and my horn stopped working. Of course I started investigating at the horn button. I finally discovered that the horn button was fine and It was grounding the horn relay circuit (found under the hood). Then I found out that the horn relay was working fine too. So, I assumed that the horn had gone bad. I did not check for voltage at the horn, because it was behind the drivers side head light. (I am sooo lazy some times.) I ordered a new horn and waited a few days for it to arrive.
It arrived, I grabbed one beer because every body knows this is a one beer job. I removed the head light and found that there was nothing wrong with the horn. The wire that connected to the horn had worked it’s way loose.
There I was, ready for a horn party and nothing needing installation. I installed the new horn anyway, now I have two!! (it is only a little louder)