High tension leads or high tension cables are car components. They are the wires which go from the Ignition coil to the Distributor and the wires which go from the distributor to each of the spark plugs. Tension in this case is a synonym for voltage, the cables therefore carry a high voltage. HT Leads, like many car components, can wear out over time. Each lead contains only one conduit, as the current does not return through the same lead, but through the earthed/grounded engine which is connected to the opposite battery terminal.