(a) Except as provided by Subsection (b), an operator required to give a stop or turn signal shall do so by:
(1) using the hand and arm; or
(2) lighting signal lamps approved by the department.
(b) A motor vehicle in use on a highway shall be equipped with signal lamps, and the required signal shall be given by lighting the lamps, if:
(1) 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 is more than two feet; or
(2) the distance from the center of the top of the steering post to the rear limit of the body or load, including the body or load of a combination of vehicles, is more than 14 feet.