(1) Turn signal lamps visible to approaching or following drivers must:

(a) Flash at a rate of sixty to one hundred twenty flashes per minute.

(b) Flash in unison. Except that a turn signal consisting of two or more units mounted horizontally may flash in sequence from inboard to outboard. The lamps may either be extinguished simultaneously or lighted simultaneously.

(c) Be mounted and operated as follows:

(i) On motor vehicles, turn signal systems must:

(A) Have four separate lamps consisting of at least two single-faced or double-faced turn signal lamps on or near the front and at least two single-faced lamps on the rear. Except that a truck-tractor or a truck chassis without a body or load may be equipped with one double-faced turn signal lamp on each side in lieu of the four separate lamps otherwise required on motor vehicles. If double-faced turn lamps are used, they must be mounted ahead of the center of the steering wheel or the center of the outside rearview mirror, whichever is rearmost.

(B) Be spaced as far apart as practical.

(C) Have the optical center of the front turn signal at least four inches from the inside diameter of the retaining ring of the lower beam headlamp unit, fog lamp unit, or passing lamp unit. Except original equipment turn signals that emit two and one-half times the minimum candela requirements may be closer.

(ii) For motorcycles, the front and rear turn signal lamps must be at least nine inches apart, except that front turn signals on motorcycles manufactured after January 1, 1973, must be at least sixteen inches apart.

(iii) On the rearmost towed vehicle in combination of vehicles, turn signal systems must be equipped with at least two single-faced turn signal lamps on the rear. The signal system on a combination of vehicles towed by a motor vehicle equipped with double-faced front turn signal lamps may be connected so only the double-faced turn signal lamps on the towing vehicle and the signal lamps on the rear of the rearmost vehicle are operative.

(2) Side turn signal lamps must:

(a) Meet SAE Standard J914.

(b) Be mounted on the side not lower than twenty inches or higher than seventy-two inches.

(c) Flash with the front and rear turn signal lamps on their respective sides of the vehicle. On vehicles with sequential turn signal lamps, the side turn signal lamps must flash with the front turn signal lamps.

(d) Flash with the rear turn signal lamps, if the side lamps flash when the hazard warning switch is actuated.