Abstract: System for selectively applying the brakes of a towed vehicle by controls in the towing vehicle; the system including a portable air compressor and a pneumatic cylinder that can be rapidly installed by attaching to a support structure on the floor of the driver's cockpit in the towed vehicle; the piston of the cylinder being attached to the brake pedal; and a three-way solenoid valve to permit or not to permit the admission of compressed air to the cylinder.