The outer magnetic circuit consists of a rolled-up tape of electrical steel. The coil housing is made of steel and has a cylindrical shape. The housing is hermetically sealed with a cover made of insulating material. Transformer oil is poured into the housing to improve cooling and insulation. A high-voltage and two low-voltage terminals are made in the coil cover. The high-voltage terminal is connected to the secondary winding and, through a contact bolt and spring, to the core. The end of the primary winding is connected to one low-voltage terminal of the coil, connected by a wire to the contact group of the ignition distributor. Voltage from the ignition switch is supplied to the "+B" terminal of the coil.
The current flowing through the primary winding of the ignition coil creates a magnetic field around the coil turns. When the breaker contacts open, the current in the primary coil circuit disappears, the magnetic field is sharply reduced and, crossing the turns of the primary and secondary windings, induces an electromotive force (EMF) in them proportional to the number of turns. In the secondary winding, the EMF reaches 12,000-24,000 V, and in the primary - 200-300 V.
The contactless system uses coils of type 27.3705 (open-circuit, oil-filled) or type 3122.3705 (with closed magnetic circuit, dry).
The original is available on the online resource: VazBook