The ignition (or distributor) cap is where ignition wires that run to the spark plugs receive high-voltage current from the ignition coil. Metal contacts in the cap connect with contacts in the ignition wires to form an electrical link, and the current is passed along to each spark plug according to its firing order. This type of ignition system with a separate ignition coil — a rotor in a distributor that sends electrical current to each spark plug through wires in the cap — began to phase out in the 1970s. Most modern ignition systems don’t need a distributor because of advances in electronic controls. They have separate ignition coils for each cylinder that connect directly to the spark plugs or, in some instances, one coil for every two cylinders and short ignition wires from the coils to the spark plugs.
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