The coil consists of an iron core around which are wound the primary, or low tension, and the secondary, or high tension windings. The duty of the coil is to convert the battery voltage of 6 or 12 to something in the order of 6,000 volts which is required to form a spark across the plug points. When the ignition switch is “on” current flows from the battery through the primary winding. This current is interrupted by means of the contact breaker, causing a high voltage to be induced in the secondary windings. The distributor moulding is provided on the inside with metal inserts, which are in contact with the high tension cables connected to the sparking plugs. The centre terminal of the distributor moulding is connected, on the outside, to the high tension terminal of the coil and on the inside it is connected by means of a carbon brush contact to a rotating distributor arm.