The ignition coil is made of two sets of windings (primary and secondary), two primary terminals (low voltage connections), an iron core (long piece of iron inside the windings), and a high voltage terminal (coil wire connection).

The primary winding is the outer winding and is made up of several hundred turns of heavy wire, wrapped around or near the secondary winding. The secondary winding is the inner winding and is made up of several thousand turns of heavy wire located inside or near the primary winding. The secondary windings are wound in the opposite direction of the primary, and the ends are attached internally to the primary windings and the high voltage terminal. Both windings are wrapped around an iron core and are housed inside the coil case.

To obtain the high current required for ignition, battery current flows through the ignition coil primary windings producing a strong magnetic field. The action of the iron core strengthens the magnetic field.

Figure 2-43.- Ignition switch and positions.

Figure 2-44.- Sectional view of an ignition coil.

When the current flowing through the coil is broken (the primary circuit is opened), the magnetic field collapses across the secondary windings. As the magnetic field collapses, a high electrical voltage is induced into the secondary circuit.

Since both the primary and secondary windings of the coil are stationary, some means other than movement of the windings must be found to change the magnetic field surrounding the coils. In practice, a switching device in the primary circuit creates this effect. There are two common methods to break current flow and fire the coil- mechanical contact points or an electronic switching device.