Sometimes this coil fires the ignition coil directly, sometimes it acts as a crank position sensor telling the CDI unit where the crankshaft is in its rotation cycle. With older outboards where the exciter coil fires the ignition coils directly, this coil will move as the throttle is opened to advance the timing of the spark mechanically. With modern ignition, the CDI unit will decide the timing based on the current RPM and the crank position sensor.