The primary components of the automotive ignition system are:
The battery supplies the Electro-Motive Force (EMF) to the ignition circuit. The battery needs a constant flow of air around it to keep it cool, and must be well maintained if it is to keep the ignition system functioning properly.
The spark plug creates the spark that ignites the air/fuel mixture inside the cylinder when the spark jumps from the central electrode to the side electrode.
Engine manufacturers include timing marks on their engines, so that the technician can check and adjust the engine timing if some conditions have changed.
The distributor has been an integral component of an ignition system for many years. But, with todays advances in electronics, it is being phased out.
Its primary function is to distribute the spark to the spark plugs in the correct sequence and at the correct time.
To complete the distributor assembly, a distributor cap and rotor are fitted.
There are many sources for the production of the high-tension spark. In this case it is in the form of an ignition coil. In this coil the primary and secondary terminals are connected inside the can.
Coils and Coil Packs are basically step-up transformers, increasing the vehicle's 12-volt supply to the voltage required to fire the spark plugs.
High-tension leads are also known as HT Leads, and connect the spark distribution unit to the spark plugs. The High Tension spark travels from the source along these leads, and jumps across the spark plug gap. This ignites the air-fuel mixture in the cylinders.
With the higher voltages that today's electronic ignition systems have to endure, the insulation material on the HT leads is now much thicker than in earlier models.