A control system for the fuel pump of an internal combustion engine includes a fuel determining network which controls the conduction of an output transistor by way of an input transistor. A transducer provides an operator demand signal to the network. In the event of failure of the network the transducer is arranged to control the supply of base circuit to the output transistor so that the conduction of the output transistor is directly controlled. The output transistor controls the flow of current in the winding of an actuator for the control member of the fuel pump.