Exactly, how does a coil work?

     The primary winding of an ignition coil is wound with a small number of turns of thick wire (approximately 200 turns) and has a small resistance. Applying 12 volts DC causes current flow.

     The secondary coil has a much larger number of turns of thin wire (approximately 20,000 turns) causing the effect of a step-up transformer.

     The coil produces a large voltage spike when the current to the primary coil is interrupted. Since the induced secondary voltage is proportional to the rate of change of the magnetic field through it, opening a switch quickly in the primary circuit to drop the current to zero will generate a large voltage in the secondary coil according to Faraday's Law. The large voltage creates a spark across the spark plug which in turn ignites the fuel mixture in the cylinder chamber.

     Today's ignition systems use a transistor switch to interrupt the primary current. An ignition control module or TCI or CDI unit handles the switching process allowing the secondary coil to increase voltage to spark plugs.

     Coils are basically step-up coils or * transformers that function using Farady's Law of Induction.

     * A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors -- the transformer's coils or "windings".

     Faraday's Law:

     Any change in the magnetic environment of a coil of wire will cause a voltage (emf) to be "induced" in the coil.  EMF (Electromotive Force)

     Why is Resistance so important?

     Any vehicle that has an onboard computer utilizes resistive ignition secondaries protection of that computer from RFI (Radio Frequency Interference) and backfeed issues. Virtually every powersport vehicle has resistors or resistance protection.

     What is Resistance?

    " Electric Resistance" - a material's opposition to the flow of electric current; measured in ohms (Ohms Law).