73 duster horn relay ?

My horn doesn't work, I've tested it across a battery and it works fine, i've cleaned where it grounds to the body, the violet wire on the 4 pin relay is hot. The car has a grant gt steering wheel, i pulled the horn push out and there's no wires, so i pull the steering wheel off and the wire from the circular connection has been cut, so i 've soldered a wire on, fed it through to the horn push but still nothing. Anyway, I took the 4 pin relay off, push the 3 pin connector onto a 3 pin relay I have spare and the relay is buzzing continually but the horn still isn't working.
Any ideas please ?