a marine vessel propulsion system includes one or more drive systems , each including an engine , an engine throttle , and a shiftable transmission . a control system for each drive system comprises a manually operable control lever assembly for electrically operating a servo assembly which mechanically operates the engine throttle and the transmission shifting clutches . the control lever assembly comprises a one - piece plastic support base which is adapted to pivotally support one or two identical one - piece plastic control levers . components associated with a control lever are interchangeable and identical and include a potentiometer mechanically interconnected between the control lever and the base , a detent plate and a detent arm . the control lever assembly also comprises based - mounted components including a station selector switch , a mode selector switch , an electrical connector and a flexible circuit board for electrically connecting the potentiometer selector switches and electrical connector . the servo assembly comprises a plastic housing containing two identical servo units for mechanically operating the engine throttle and the transmission shifting clutches . each servo unit comprises a support frame on which are mounted a reversible electric motor having a rotatable motor shaft , a rotatable link - drive shaft and a solenoid - operated clutch for connecting and disconnecting the motor shaft and the link - drive shaft . a potentiometer mechanically connected to the link - drive shaft is restrained from rotation by a clamp engaged with the motor housing .