The distributor cap is a device in the ignition system which distributes electricity from the ignition coils with the spark plug wires at the appropriate time. The distributor cap is usually made of hard plastic and a small amount of copper. Inside the distributor cap is the distributor rotor which rotates as it receives current from the ignition coils and transmits it to the copper portion of the cap, and then it passes to the spark plugs.
The distributor rotor also has a metal component allowing it to connect to the spark plug and cylinder wires in the engine. The rotor is mounted on the upper end of the distributor shaft and it is fixed by two screws to a plate on the upper part of the shaft. The rotor is embodied to the locators that perfectly fit into the holes in the plate so it won’t fall off. A centrifugal advance mechanism moves the rotor by rotating the camshaft.
The distributor cap is subject to high voltage discharge all the time; therefore it must be periodically inspected and replaced. It is suggested to change it every two years or every 24,000 km. The older vehicles are more likely to have this spare part failed.
ES 
EN