Any motor vehicle may be equipped with not more than two side cowl or fender lamps which shall emit a white or yellow light without glare. Any motor vehicle may be equipped with not more than one running board courtesy lamp on each side thereof which shall emit a white or yellow light without glare. Any motor vehicle may be equipped with a back-up lamp either separately or in combination with another lamp; except that no such back-up lamp shall be continuously lighted when the motor vehicle is in forward motion.