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