I assume that you are referring to the original, 6V horn on your '50 half-ton? I'm not positive if it is like the horn on the '52, but if so, it should be mounted to your exhaust manifold and there should be two wires running to it (See photo attachment). It is a strange mount, because the screws holding it to the manifold are electrically insulated from the horn. One wire is 6V and the other is ground. There should be voltage present at all times on one wire. The other wire (ground) runs up through your steering column. When you press the horn button, it provides the ground for the circuit. I'll bet that the grounding plate, just behind the horn button, is dirty or corroded. When I bought my truck that was the reason my horn wouldn't work at all. Took me forever to track that down. Now, about once per year I will notice my horn starting to sound weak (it's almost embarassing). I will pop off the horn button with a screwdriver and that gives you access to the "switch." You should see a round, metal plate held on by the same nut that holds on the steering wheel. Remove that nut, and also the wire attached to the plate and then remove the plate. You will notice that it is actually two steel discs, slightly separated. If you squeeze one edge of the assembly, you will see the two discs come together and make contact. In your truck, that contact is what provides the horn's ground. There are small screws (three I think) that hold those two plates together. Removed those screws, separate the plates, and clean both surfaces with acetone or some other, non-oily solvent. If either is corroded, remove the corrosion with emery paper. Put it all back together and I'll bet your problem will be solved.
