Distributor Cap for the Lucas distributor fitted to the four-cylinder petrol engine, part of the ignition system.

The cap seats over the distributor body and carries the high-tension current from the rotor arm to each spark plug lead in turn, distributing the spark to the cylinders in firing order. The central king-lead terminal feeds the coil output to the rotor beneath. A cracked or internally tracked cap causes misfires and hard starting, so it is renewed as part of routine ignition servicing.