NRS 484D.265
Equipment for towing vehicle.
1.
Every towing vehicle, when used to tow another vehicle equipped with air-controlled brakes, in other than driveaway or towaway operations, shall be equipped with two means for emergency application of the trailer brakes. One of these means shall apply the brakes automatically in the event of a reduction of the towing vehicle air supply to a fixed pressure, which shall be not lower than 20 pounds per square inch nor higher than 45 pounds per square inch. The other means shall be a manually controlled device for applying and releasing the brakes, readily operable by a person seated in the driving seat, and its emergency position or method of operation shall be clearly indicated. In no instance may the manual means be so arranged as to permit its use to prevent operation of the automatic means. The automatic and the manual means required by this section may be, but are not required to be, separate.2.
Every towing vehicle used to tow other vehicles equipped with vacuum brakes, in operations other than driveaway or towaway operations, shall have, in addition to the single-control device required by NRS 484D.270, a second control device which can be used to operate the brakes on towed vehicles in emergencies. The second control shall be independent of brake air, hydraulic and other pressure, and independent of other controls, unless the braking system is so arranged that failure of the pressure upon which the second control depends will cause the towed vehicle brakes to be applied automatically. The second control is not required to provide modulated braking.
Source:
Section 484D.265 — Equipment for towing vehicle., https://www.leg.state.nv.us/NRS/NRS-484D.html#NRS484DSec265.