Question: what does a distributor cap and rotor do

title: Distributor
text: The rotor is attached to the top of the distributor shaft which is driven by the engine 's camshaft and thus synchronized to it . Synchronization to the camshaft is required as the rotor must turn at exactly half the speed of the main crankshaft in the 4 - stroke cycle . Often , the rotor and distributor are attached directly to the end of the one of ( or the only ) camshaft , at the opposite end to the timing drive belt . This rotor is pressed against a carbon brush on the center terminal of the distributor cap which connects to the ignition coil . The rotor is constructed such that the center tab is electrically connected to its outer edge so the current coming in to the center post travels through the carbon point to the outer edge of the rotor . As the camshaft rotates , the rotor spins and its outer edge passes each of the internal plug terminals to fire each spark plug in sequence .