An electronic control is provided for controlling the drive speed of a supplemental drive relative to an engine driven main drive of a vehicle. A fluid pump driven by the engine provides pressurized fluid flow. The supplemental drive is driven by the pressurized fluid. A main drive sensor senses the speed of the main drive and responsively produces a main drive speed signal. A command knob is provided for selecting a desired speed relationship between the main and supplemental drives. A knob sensor senses the position of the command knob and responsively produces a modifier signal. A modifier circuit receives the main drive speed and modifier signals and responsively produces a modified main drive speed signal. A supplemental drive sensor senses the speed of the supplemental drive and responsively produces a supplemental drive speed signal. A processor produces an error signal responsive to a difference between received modified main and supplemental drive speed signals. The processor produces a first signal responsive to a product of the error signal and a preselected constant, produces a second signal responsive to an integral of the error signal, produces a third signal responsive to a derivative of the error signal and produces a pump control signal in response to a sum of the first, second, and third signals. An actuator receives the pump control signal and responsively adjusts the pump output.