321.432  Horns and warning devices.
  Every motor vehicle when operated upon a highway shall be equipped with a horn in good working order and capable of emitting sound audible under normal conditions from a distance of not less than two hundred feet, but no horn or other warning device shall emit an unreasonably loud or harsh sound or a whistle. The driver of a motor vehicle shall when reasonably necessary to insure safe operation give audible warning with the horn but shall not otherwise use such horn when upon a highway.
[S13, §1571-m17; C24, 27, 31, 35, §5040, 5041; C39, §5034.41; C46, 50, 54, 58, 62, 66, 71, 73, 75, 77, 79, 81, §321.432]
For applicable scheduled fine, see §805.8A, subsection 3