The first versions were low tension coils, then low-tension and in turn high-tension magnetos, which were offered as a more effective alternative to the older-design hot-tube ignitors that had been utilized earlier on hot tube engines.
Manufacturers such as Ford, General Motors, Chrysler, Citroen, Mercedes, John Deere, International Harvester, and many others incorporated them into their products.
A magneto is one of the electromechanical devices invented for the purpose of ignition with gasoline internal combustion engines.
As the current flows, the wire loops develop their own magnetic field, which takes a certain amount of energy to form.
This voltage jumps across the gap of either the ignitor or a spark plug located in the combustion chamber and ignites the air–fuel mixture to do work.
When the contact breaker opens the circuit, the magnetic field collapses, causing a high electric voltage in the primary and secondary coils.
They are also used on drag race cars because they offer a weight advantage over systems that utilize a distributor and battery.
This high voltage was carried or "distributed" by a distributor to each of the multiple spark plugs in a gasoline car or truck engine.