The primary ignition system includes all of the components and wiring operating on the low volt side of the circuit.

Wiring in the primary circuit uses conventional wire, similar to the wire used in other 12 volt electrical circuits.

So, all ignition coils have two set of windings, the primary ignition system side and the secondary ignition system side.

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The primary ignition system may contain any of the following components:

Ignition Key Switch:

  • Supplies power from the battery to the ignition system.


  • Supplies low voltage current to the primary ignition coil during startup. Once the engine is running, low voltage current is provided by the alternator.


  • Once the engine is running, low voltage current is provided by the alternator.

Starter Motor:

  • Engages the engine’s flywheel to rotate the engine during startup.

Ignition Coil (“Conventional” ignition systems):

  • A high-voltage transformer made up of two coils of wire, the primary coil and the secondary coil; provides high voltage current to the distributor.

Ignition Coil Pack (“Distributorless” ignition systems):

  • Essentially a “group” of ignition coils, with each coil providing high voltage current to a single spark plug.

Breaker Points (“Conventional” ignition systems):

  • “Interrupt” current flow to the primary ignition coil.

Distributor (“Conventional” ignition systems):

  • Distributes the high voltage output of the ignition coil to the cylinders/spark plugs at the correct time.

Spark Plug:

  • Uses the high-voltage electricity generated by the ignition coil to generate a spark to ignite the air/fuel mixture.

Ignition Module (“Distributorless” ignition systems):

  • Receives signals from the crankshaft sensor and camshaft sensor, as well as the spark signal from the vehicle’s ECM.

Crankshaft Timing Sensor (“Distributorless” ignition systems):

  • Sends a signal that supplies timing and RPM information to the ignition module and the vehicle’s Engine Control Module (ECM).

Camshaft Sensor (“Distributorless” ignition systems):

  • Supplies information related to cylinder position for the ignition coils and fuel system.

Diagnosis Testing Tips

So, if the ignition system does not work (no spark) you can test it with a 12v test light. It will confirm that electric current in the primary ignition system is getting turned ON and OFF. Hook up a 12 volt test light between the positive battery terminal and the negative side of the ignition coil. As a result, we can easily see if primary current is tuning ON and OFF. Your test light will turn ON when current is flowing and turn OFF when the current has stopped.

This is easy to see at cranking speeds (200 – 300 RPM). Consequently, if the test light does not turn ON, or it never turns OFF, we know its the primary ignition system. We don’t know exactly what is wrong but we have narrowed our search to the primary ignition system. You may also see that the primary current is turning on and off, but there is no spark. In that case the problem is likely in the ignition coil, or in the secondary ignition system.

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