456A.12  Lighting by law enforcement vehicles of conservation officer.
  The required usage of lighting devices set out in sections 321.384 through 321.409 and section 321.415 does not apply to official law enforcement vehicles operated by conservation officers appointed under section 456A.13, while these vehicles are being used in criminal investigations or while attempting to apprehend suspected criminals.
88 Acts, ch 1216, §43
C89, §107.12
C93, §456A.12