Distributor Cap: Description and Operation

The distributor cap is clipped or screwed onto the top of the distributor and the spark plug wires plug into the insulated terminals on top. The cap provides a means of separating the ignition wires so that the spark energy from the ignition coil can be distributed to the correct cylinders at the proper time.
Some distributor caps also have a cover that clips on with the cap. This cover provides radio static suppression so the high energy sparking that occurs inside the cap does not interfere with radio transmission/reception.