When diagnosing a horn issue I always start by hooking them directly up to a battery and see if it is the horn or the wiring at fault.
- Open the horn coil cover and unclip the two wires.
- Run test wires from the battery clipping the negative to to horn bullet clip
- Touch the other wire to the other horn bullet clip
This will tell you if the horn is good. If it is you now need to check the wires for continuity.
- Check the 12 gauge yellow wire back to the battery
- Thread a yardstick up through the steering wheel, bending it and then down again through the steering wheel rim. This will push the horn button in and ground the it
- First check from the horn black-yellow wire at the horn to any ground.
- If this indicates high resistance, undo the horn-light switch
- Now check from the same horn terminal to the middle button of the switch
- Also check from the soldered end of the horn rod to ground.
This is the wiring diagram for my 1932