The wiring on the relay should be as follows
H = "Red" to horn terminal
B = "Dk Blue" To amp meter 12v
S = "Blue"To horn button (this is the wire coming out of the steering column.
Yellow wire is the ground from the engine to the horn bracket. Make sure you have a good ground for it to work properly.
The wiring from the horn button I believe is blue that runs to the "B" terminal on the relay.
By Capri has 12v and is a late 1957.
I do not know if the horn is original but it was mounted in this area inside the engine hatch. As you can see the relay was also changed. These two parts I believe tended to go out.
Hope it helps