Horn wiring Ford Cab 12 8cwt
 

Having located where the horn should go from my other thread I now need some help on the wiring. The wiring diagram is not much help.
The horn has just one terminal (unlike my jeep which has two). There is the stub of one wire poking out from the base of the steering column. I believe the horn gets power from the starter solenoid battery connection but what's the rest of the story?

There'll be a horn relay solenoid somewhere. When the horn button grounds the wire in the steering column the relay clicks and sends power to the horn.