Mont. Code Ann. § 61-9-216

A vehicle, including animal-drawn vehicles and vehicles referred to in 61-9-109 (4), not specifically required by the provisions of this chapter to be equipped with lamps or other lighting devices, must at all times specified in 61-9-201 be equipped with at least one lamp displaying a white light visible from a distance of not less than 1,000 feet to the front of the vehicle, and with two lamps displaying red light visible from a distance of not less than 1,000 feet to the rear of the vehicle. The vehicle may have one lamp displaying a red light visible from a distance of not less than 1,000 feet to the rear and two red reflectors visible for distances of 100 to 600 feet to the rear when illuminated by the upper beams of headlamps.