(a) Any stop or turn signal when required herein shall be given either
by means of the hand and arm or by signal lamps, except as otherwise
provided in paragraph (b).
(b) Any motor vehicle in use on a highway shall be equipped with, and
required signal shall be given by, signal lamps when the distance from
the center of the top of the steering post to the left outside limit
of the body, cab or load of such motor vehicle exceeds twenty-four
(24) inches, or when the distance from the center of the top of the
steering post to the rear limit of the body or load thereof exceeds
fourteen (14) feet. The latter measurement shall apply to any single
vehicle, also to any combination of vehicles.