Mont. Code Ann. § 61-9-309

A motor vehicle, trailer, semitrailer, or pole trailer, and a combination of these vehicles, except motorcycles, quadricycles, and motor-driven cycles, equipped with brakes must have one control device that can be used to operate all service brakes. This requirement does not prohibit vehicles from being equipped with an additional control device to operate brakes on the towed vehicles. This regulation does not apply to driveaway or towaway operations unless the brakes on the individual vehicles can be operated by a single control on the towing vehicle.