NGK Ignition Coils Essentially the operating principle is essentially the same for all types whether the classic can-type coil, or in a coil rail system. The device contains two copper wire windings and a laminated iron core. The copper wires are insulated to prevent short circuits. The battery current fed through the primary winding produces a magnetic field whose strength is further increased by the iron core. When this circuit is opened, the magnetic field collapses, inducing a high voltage pulse in the secondary coil. This pulse is fed through the H.T. connection to the spark plugs. As an integral part of the ignition system, the coil produces the high voltage required to produce the electric spark to ignite the fuel. The relatively low battery voltage, nominally around 12 V, is transformed to up to 45,000 V.