My cougar only has one horn working, the passenger side, that aims down. The driver side, aims up. If i plug it, All i get is a kind of gurgle, and no horn. If i unplug the driver’s side, the passenger side horn works.
Granted, only one side does sound pityful, but it is legal.
I can see a H circled, just above the Delco Remy writing (made in canada eh? 
). Do i order a High note one?
Funny! Almost exactly the same as my 68. Passenger horn works if driver horn is disconnected, driver horn doesn’t work at all and if it’s connected the passenger horn doesn’t work either. I think I’d rather have two Low horns than a Low and a High. Or a Low and an Even Lower.
I replaced mine with horns from a later model Ford product. Same style horns, just had to tweak the bracket a bit to make it look like the original
I did a fair amount of searching, and, the best advice (apart from “sticking your ear to it and getting someone to blow the horn” which usually assures it will work) was to try the horn directly on the battery. Actually scared the bejesus out of me. it works louder than the other one. There was something “loose” feeling inside, but i slapped it around a bit, and when nothing sounded loose, it worked just fine. the passenger side now sounds a bit less, but the combination of both doesn’t sound pityful anymore.
The horn ground through the mounting bolt. That area needs to be clean to make good contact. It is something that is often overlooked.