The orange wire on the horn supplies power to the internal coil and the internal switch.
When the button is depressed the circuit for the coil is completed, energizing the coil and closing the internal switch. When the switch is closed, power travels thru the switch and to the horn.
Sometimes the horn diode will fail and allow the horn to sound at all times. Also the noise suppressor at the horn goes bad, not allowing current to get to the horn. Just remove it. Only needed with military radios.
Areas to check for non-horn operations are:
horn button
steering column wiring connector
relay contacts
firewall connection
noise suppressor
horn connection
Here is the horn diagram.
