Abstract: Apparatus for developing and applying sparks to the combustion chamber of an internal combustion engine. The apparatus comprises separate primary and secondary winding units. The secondary unit includes a spark plug having an insulator. The insulator carries a secondary coil winding which is connected to the electrodes of the spark plug. The insulator has a bore which contains a magnetic core for the secondary winding. The primary winding unit includes a primary winding and a tubular flux carrying part formed of magnetic material. The primary winding unit has a bore which is slipped over a portion of the secondary unit that has the secondary winding. A voltage is induced in the secondary winding by magnetic coupling to the primary winding when it is energized.