Your car engine has a coil, which is basically a high-voltage transformer composed of two wire coils. One of the coils is referred to as the primary coil, and the secondary coil wraps around it. There are hundreds of times more turns of wire on the secondary coil than on the primary coil. The battery's current runs through the primary coil.

When a solid-state device in the electric ignition disrupts the current suddenly, it's referred to as breaker points. The breaker points are what make the coil work properly. When the circuit is broken abruptly, the magnetic field collapses and the secondary coil is overtaken by the powerful magnetic field. Since there are so many windings in the secondary coil, the magnetic field causes an incredibly high-voltage current of up to 100,000 volts to rush through it. Then the secondary coil passes the voltage on to the distributor along a well-insulated wire.

Occasionally, mechanics are faced with mysterious engine problems that they can't pinpoint. Such problems are often caused by worn-out spark-plug wires that lose some of their insulation, due to the high voltage being passed through them from the coils. When you take your car in for a tune-up, you normally replace the cap and rotor. The rotor connects to the coil and it spins inside the cap. When the rotor spins past contacts in each cylinder, the coil sends a high-voltage pulse across a gap between the rotor and contact. The spark then travels down the spark-plug wire to the correct spark plug in the proper cylinder. Any malfunctions in this setup could be a result of ignition coil failure. All of these parts are subjected to a lot of wear and tear, thanks to the intense electricity passing through them.