Spark plug wires

Spark plug wires (also called high tension leads) are electrical cables used by older internal combustion engines to transmit high-voltage electricity from the distributor to the spark plugs .

Spark plug wires have an outer insulation several times thicker than the conductor, made of a very flexible and heat-resistant material such as silicone or EPDM rubber.

Dielectric grease can be used to improve insulation; a small amount can be applied in the inside of the rubber boot at each end of each wire to help seal out moisture.

To reduce radio frequency interference (RFI) produced by the spark being radiated by the wires, which may cause malfunction of sensitive electronic systems in modern vehicles or interfere with the car radio, various means in the spark plug and associated lead have been used over time to reduce the nuisance: Older ignition systems with a separate ignition coil use a coil wire between the ignition coil and the distributor.

Many modern car engines use coil-on-plug ignition, which eliminates the need for spark plug wires.