[davepl]

1) Get your wife to come out and hold onto the wingnut
2) Press horn button in cab

Are you in serious trouble? Then the relay works.

If that doesn't prove conclusive, here's a diagram. Sadly I don't know which terminals are which on the actual relay or I'd give you some steps to try.... I believe the horn circuit wire is usually green, which triggers the relay to pass current through the main lug.