Starter Controls - BOSCH: Description

Bosch Starter (Solenoid) switch is used on pre-engaged screw-push starter motors. Mounted on starter, solenoid activates a soft iron plunger (armature) which is connected to the overrunning clutch shift lever, in starter motor. Two coils are used in the solenoid. A "pull-in" coil to engage starter and a "hold-in" coil to hold cranking starter into flywheel. After cutting in starter motor current, the pull-in coil is short circuited, and only hold-in coil remains energized. When starter motor is switched off, current to solenoid stops and armature returns to outer position.