Classic/Antique Car Repair: 1970 mustang horn, bench test, battery connection

Question
Horn S stop working, have bench test the horn and check the relays in steering column, any advice would be great.

Answer
Follow the two wires that go out to the horns, back to the small black metal relay box with 3 terminals that they are connected to.  The 3 terminals are H (the horn connection) B (the battery connection) and S (the switch connection).

Verify that there is 12 volts on the B terminal, and that the horns and the relay box are securely grounded (bare metal incontact with each device).  Then ground the "S" terminal with a wire to ground.  This should sound the horns.  If so but your horns don't work from the steering wheel, your problem is either a disconnected "S" wire or a bad switch inside the horn actuating assembly on the steering wheel.  

You'll just have to take it apart and track down what is disconnected in there.  When you ground the black wire that comes up to the steering wheel contacts, the horn should sound.   If you can ground it manually (by touching the end of the wire to ground) everything electrical is OK, the problem is the contact inside the steering wheel is dirty, disconnected, or broken.

Dick