Your horn may be intermittent due to worn slip rings between the steering wheel and column. Not a terribly difficult operation to replace, parts are about $74.00 and requires complete disassembly of the steering wheel. Unless you need the horn to pass a State inspection you can wait until the horn completely ceases to function before repairing.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.