Mercury Mariner Outboards 2.2 / 2.5 / 3.0 Service Shop Manual, Page 20Get this manual
Description When the breaker points are closedmagnetic field is built up in the primary coil (located below flywheel) as the flywheel permanent magnets pass the coilWhen breaker points open, the magnetic field of the primary coil collapses, discharging voltage into the primary winding of the secondary coil At this same timethe condenser also discharges its stored voltage into the primary circuitThis current creates an extremely high voltage in the secondary coil that will jump the spark plug gap