Hi CollinR Reading about your initial complaint , I see it not making any sense , the item you show in your photo (3764548) is the Key/In seatbelt buzzer. Your horn relay is mounted on the relay block near the fuse block and is a metal can design. There are a few differences in that relay , IF you have the New York city Horn option then you will have a five terminal relay. If not, you will have the conventional three terminal as shown by Big John (P/N 3764643 ). The little yellow buzzer you show is activated either by the Key switch in the column or by the seat belt interlock module. The interlock module reacts to two switches in the seat , either a beam switch right under your Derrier or by the seat belt switch in the buckle. You will get a buzzer operation and a seat belt warning light until you fasten your belt ,then it should shut up. Door Adjar Buzzer operation and the door Adjar light is activated by a set of switches mounted on the door frame of each door. They are those black button like things , the same annoying buzzer is used with activation origin from the seat belt interlock module. So in short the seat belt Buzzer is a separate entity from the horn. So why does your Chronometer not work? Well its fed by the same fuse that feeds the Horn , so you need to check cavity no. 4 in the fuse box to see if the fuse is intact, if not , that's why your horn no longer works and something caused it to blow. Your seat belt buzzer etc. is fed from fuse cavity 5. The door Adjar switches have one wire going to them with the case grounded by the mounting screws. So you see they are two separate entities.
So...reconnect the buzzer and then go around to each door Adjar switch and remove the small Phillips screws and pull out the switch just a bit so the contact to ground is broken the buzzer should shut up , re install the screws/ switch one at a time to isolate the culprit.
With that out of the way you can concentrate on the Horn. The reason you could not locate a replacement Buzzer is that Chrysler would stamp a part number on the buzzer or relay as a "production number" To locate the part you had to have the "service" number in each parts book there was a table giving you a cross reference from production to service numbers.