Ignition leads connect the distributor to the spark plugs and therefore form an important part of the overall car engine ignition system. Ignition leads or cables carry the High Tension Voltage from the ignition coil that is required for the spark plugs to ignite the air/fuel mixture. It's important that the HT Voltage is not allowed to escape before reaching the spark plugs. Faulty ignition leads, due to perished, torn or chaffed cable insulation and dirty cable connectors are common causes of rough running, misfires, high fuel consumption and NCT emissions failures.
What type of ignition lead you need will depend on your model of car and the type of spark plug it uses.