As already said, coils are voltage transformers, there are two different uses of them, step up and step down. Our cars use step up transformers for DC low voltage, high current, (check out Ohms law )DC = direct current. They are made of solid small gauge wires wound around a piece of conductor materail to make them work,they are filled with oil to help keep them cool Cool being relative Coils usually fail because a of a broken wire, not a burnt up wire Coils designed for multi spark ignitions have a different ratio(numbers ) windings internally than standard coils do Different loads need different parts The ballast resitor is a solid wire resitor used to reduce the voltage input into the coil, the only time it is not working is when a ground is applied to that circuit for the current to flow through the coil, once for each firing stroke, 8 times per cycle (RPM) on V8 motors Are you confused yet