Distributor caps are ignition system components found in vehicles with distributor-based ignition systems, typically pre-2000 models. They house the rotor and distribute high-voltage from the ignition coil to the correct spark plug, timed to the engine’s firing order. Constructed of insulating material – commonly phenolic or polymer composites – they feature conductive terminals for plug wire connection and a central rotor contact. Internal carbon brushes or conductive pathways maintain electrical continuity as the rotor spins. Cap failure manifests as misfires, rough running, or complete engine stall due to compromised voltage delivery.