Horn relay mounting bracket/foot must be grounded according to 1951 diagram. You have mounted to painted surface. Attach a wire under screw to clean metal place.
Both horn brackets/housings must be grounded to clean metal place. No paint on horn bracket bottom or truck body. If the housings have a dedicated ground terminal/screw, be sure terminal wire is touching a clean horn terminal/screw and be sure other end is to clean metal spot nearby on truck.
When you add these grounds, you can't add them to another screw or bracket that is on a painted surface. To test, you can use well attached temporary wires to the battery negative terminal to see if the spark/honk/click/buzz...........goes away.
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
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