[Herb Concord Ca]

try using a multimeter set to resistance. one probe on the end metal tab on the horn rod and the other probe on ground. you should have an open, no reading on the meter. Pressing the horn button should show close to zero ohms. if you have this response, the horn rod and button works.
The one wire JC Whitney horn can be modified to work like a Model A horn by taking the cover off and carefully looking for the varnished coated wire connected to the horn frame, if you can find this connection cut the wire from the horn frame and that wire becomes your second horn wire.
Good luck