Basic Circuitry

• All ignition systems consist of two interconnected electrical circuits.

• Depending on the exact type of ignition system, components in the primary circuit include the following.

• The secondary circuit includes these components.

Ignition Components

• Ignition Coil
• • To generate a spark to begin combustion, the ignition system must deliver high voltage to the spark plugs.
  • Because the amount of voltage required to bridge the gap of the spark plug varies with the operating conditions, most late-mode vehicles can easily supply 30,000 to 60,000 volts to force a spark across the air gap of the spark plug.
  • Since the battery delivers 12 volts, a method of stepping up the voltage must be used.  Multiplying battery voltage is the job of a coil.
  • The ignition coil is a pulse transformer that transforms battery voltage into short bursts of high voltage.

• Spark Plugs
• • Spark plugs provide the crucial air gap across which the high voltage from the coil causes and arc or spark.
  • The main parts of a spark plug are a steel shell; a ceramic core or insulator, which acts as a heat conductor; one insulated in the core and the other grounded on the shell.
  • A terminal post on top of the center electrode is the connecting point for the spark plug cable.
  • Current flow through the center of the plug and arcs from the tip of the center electrode to the ground electrode.

• Ignition Cables
• • Spark plug cables, or ignition cables, make up the secondary wiring.
  • These cables carry the high voltage from the distributor and  the multiple coils to the spark plugs.
  • The cables are not solid wire; instead they contain carbon fiber cores that act as resistors in the secondary circuit.
  • They cut down on radio and television interference, increase firing voltages, and reduce spark plug wear by decreasing current.
  • Insulated boots on the ends of the cables strengthen the connections as well as prevent dust and water infiltration and voltage loss.

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