High tension leads or
high tension cables or
spark plug wires or
spark plug cables are the wires that connect a
distributor, ignition coil, or
magneto to each of the
spark plugs in some types of
internal combustion engine. "High tension lead" or "cable" is also used for any electrical cable carrying a
high voltage in any context.
Tension in this instance is a synonym for
voltage. High tension leads, like many engine components, wear out over time. Each lead contains only one wire, as the current does not return through the same lead, but through the earthed/grounded engine which is connected to the opposite battery terminal (negative terminal on modern engines) high tension may also be referred to as HT.