Abstract: A pulse width modulated control signal is applied to inlet and outlet solenoid valves in a closed fluid vehicle brake system. The electronic actuating circuitry can control a fluid brake system in a towed vehicle from a towing vehicle without fluid connections therebetween. The closed fluid brake system provides an electrical feedback signal that tracks an electrical command signal applied by the towing vehicle operator through a manually operated command signal transducer to produce an error signal to maintain a command pressure in the towed vehicle fluid brake system. The inlet and outlet valves are repeatedly opened and closed in accordance with the width of a train of pulses. The pulse width is proportional to the difference between an electrical command signal and an error signal.