The horns are junk in these cars, B210 and 210. I have 10 horns and only 2 work. I am in the process of taking them apart and cleaning the contact and any other corosion I find. I've actually fixed a couple already. Make sure you bench test any horns you may acquire with a car battery before going through the trouble of swapping them out.
I've never seen a 521 horn fail.