Here are the official words:
20.19 Horn
.
Every motor vehicle shall be equipped with a
horn (electric or air) in good working order and
capable of emitting a sound audible for a
distance of 200 feet or more, but no horn shall
emit an unreasonably loud or harsh sound or a
whistle.
Bulb or hand-
operated horn is acceptable if
original vehicle
equipment.
1. Inspection Procedure
a. Sound the horn.
b. Check actuating device.
c. Examine wiring â€" mounting.
2.
Inspect for and reject if:
a.
Vehicle is not equipped with a horn.
b.
Horn or horn switch is not securely
fastened.
c.
Wiring insulation is worn, rubbed bare,
or shows any evidence of burning, short
circuiting, or poor connections.
d.
Horn switch not readily accessible to
vehicle operator.
e.
Horn is actuated by grounding two bare
wires or similar method.
f.
Sound is not audible under normal
conditions for 2
00 feet.
g.
Horn emits an unusually loud or harsh
sound or whistle.
h.
Operation of the horn interferes with the
operation of any other circuit.
i.
Horn switch missing or inoperative