Horn issue...

I have never known, EVER for Mattox, unlike myself, to make a disparaging comment. Don't take things so personal. Ask yourself, "How old, again, are these cars?" There may be "hacked" wiring in your car that you have not seen or detected yet. Or, it may be a connector problem. For example, in the later cars, the horn relay is INSIDE the pass compartment, meaning, the full horn current must flow through a terminal in the bulkhead connector, and THAT alone can cause this disfunction.

Some things to check. Make CERTAIN the horn is staying grounded. Rust around the mounting bolt

You might adjust the horn(s) purposely. That is because the buzzer contacts can become rusty/ corroded, as well as the the screw threads, and the act of adjusting them while sounding, will sort of burn them clean. "Mark" / note the position before you turn it, so you can rough it back into shape

Horn relay does not need ground. The path for the coil is from the battery terminal on the relay, through the coil, to the horn button, and ground.

The contact of course is batter, through contacts, and to horn.

Be sure the horn flag/ push on terminals are not corroded and go on tightly. Might "work" them on/ off several times