Evidently, horn failure is pretty common in Amazons. Rather than fix the horn button, or simply disconnect the horns, the previous owner of my car (out of frustration?) went ahead and removed part of the horn switch entirely.
Figuring it'd be faster and cheaper than trying to locate a replacement, I took it as a challenge to fabricate a new switch from scratch, using a diagram from GCP as a guide.
parts 34 through 38 were missing on my Amazon
To form the main body of the switch (part 36), I soldered a 1/2" x 1/8" ring made from copper plumbing pipe to a length of 17/32" brass tubing. I sealed the other end by soldering on a piece of flattened copper pipe (I didn't have any plate handy) and drilled a hole for the wire (part 35). I found a suitable spring (part 37) from my local hardware store, along with a nylon spacer (part 38) that fit snugly inside the brass tubing. I soldered the wire to a rivet (part 34), and soldered an extra glob of tin to the rivet to give the end a little extra "crown."
(As a side note, I whacked the whole thing together in about an hour using only a drill, a pipe cutter, a hacksaw, a butane torch, and a file. I'm constantly amazed at how much you can do with basic hand tools. Then again, they made some pretty crazy stuff back in the days of antiquity, long before there was such thing as an Epilog.)
I proceeded with the standard fix of making a new foam insulator (part 23 in previous diagram) to hold the two halves (parts 22 and 25) of the horn switch apart. I got a rubber overflow washer from the plumbing section of my hardware store and cut a section out to fit the diameter of the horn ring, then glued it back together with hot glue. I had to trim the washer, which was originally 3/'8" thick, down to about 1/4" to get the correct "springiness." Finally, I punched some holes in it to fit the posts and nylon insulators.
ugly, but functional
Because the new assembly is much "springier" with the new rubber washer installed, I had to use some C-clamps to compress the whole sandwich before re-installing the clips which hold it together.
The last step in bringing my Amazon's horns back to life involved disassembling and cleaning the horns themselves. I discovered that one of the contacts inside the horns was severely oxidized. I used electrical contact cleaner and some 400 grit sandpaper to renew the contact, then treated with De-Ox before reassembling.
arrow indicates location of oxidized contact
I ran a new wire to horn switch through the steering tube (much easier to start at the steering box and feed it up through the steering tube) and hooked the whole thing up.
Honk honk! My 122 can sing again.