Ignition Lead

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2 Item(s)

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Ignition Lead

Ignition Leads

Alternatively known as a high-tension (HT) lead or spark plug wire, an ignition lead plays a vital role in an engine’s fuel ignition system. The quality of their condition can have a noticeable impact on an engine’s performance. Damaged ignition leads can cause an engine to misfire, as well as dramatically increasing emissions, potentially leading to the vehicle failing its MOT. At Green Spark Plug, we sell a wide range of ignition leads, suitable for cars old and new. 


What is an ignition lead? 

It is through an ignition lead that an electrical current is transferred from the ignition coil down into the spark plug and ultimately, lighting the fuel and air within the engine combustion chamber. Without them, a car simply won’t start. To ensure that the electrical current only flows one way, the ignition lead returns via a negative battery terminal. The high voltage of this electrical current is why some refer to ignition leads as high-tension leads.  

An ignition lead is comprised of a conductive material surrounded by a silicone jacket. The primary purpose of the silicone surround is protection. Ignition leads sit in close proximity to the engine itself and so are subject to dramatic changes in temperature, caustic chemicals and frequent abrasion. A silicone outer layer helps to protect the conductive core from external damage, extending its lifespan. The core itself, which carries the current, will either be made of copper or carbon, depending on the age of the vehicle. Older vehicles use copper, modern ones carbon. 

Why would you need a new ignition lead?

Changing an ignition lead won’t increase the power of an engine, but rather will help recover any power that has been lost over time. It’s all about transferring the energy of the electrical current in the most efficient way possible. Both copper and carbon cores deteriorate over time, reducing the amount of power that is able to reach the engine, thus compromising the ignition process. 

Generally, such deterioration is caused by simple wear and tear. The ignition leads become worn-out due to the engine’s heat and constant vibration, which can in turn loosen the connection to the spark plug. As that connection begins to come apart, energy is lost and the engine efficiency drops. More energy is thus required to generate the necessary spark to ignite the fuel and air within the combustion chamber. Fuel consumption increases and the likelihood of your vehicle passing its MOT emissions test becomes slimmer. Furthermore, the higher voltage can cause damage to both the ignition coils and spark plug itself. 

How can you tell if your ignition lead has begun to pose a problem? Look out for these signs:

  • Misfiring engine

  • Decrease in power and acceleration

  • Fuel inefficiency

  • The engine light has come on 

We would recommend that you choose higher quality ignition leads for improved durability and a longer lifespan. As a general rule, we would encourage you to change your ignition leads every five years or so, normally when you change your spark plugs. 


What type of ignition lead do you need? 

The majority of standard ignition leads for vehicles is 7mm in diameter but 5mm cable is used for mopeds and garden tools and 9mm cable is used for veteran cars. 

At The Green Spark Plug Company, we have a vast range of HT lead. Most of it is copper or tinned copper core which has no resistance. Spark plug caps with a wood screw fitting (to screw the HT lead into) are generally used for the copper or tinned copper core cable. 

The resisted cable has a graphite core. If you use graphite cable it is advised that you use a terminal for the plug end such as HT5 or HT4. If your distributor or coil is a push in fitting use the HT13 as this is the easiest terminal to fit.


If you have any questions about which ignition lead is suitable for your vehicle type, please do get in touch