You may have already solved this but here is a wiring diagram for 1951 Chevy passenger vehicles from the Old Online Chevy Manuals maintained by Keith Hardy. Lots of free info here. Here you'll find two horns and a horn relay diagrammed. This is just a pictorial of what Toyvo was telling you. Good luck with your ride. Let us know how it is going.

http://chevy.tocmp.com/1949_53shop/12electrical/12_04.HTM


"Nothing astonishes men so much as common sense and plain dealing." - Ralph Waldo Emerson