HT Leads


Does your vehicles engine misfire, does it judder due to a running problem?

This could be a HT lead breaking down or it may have a weak spark for some other reason. If your vehicle has a running problem, from our workshop in Chatham in Medway we have the knowledge and capability to test for a spark to see if the HT leads are faulty.

What are HT leads?

High tension leads are more commonly referred to as HT leads. They are the wires that connect a distributor or ignition coil to each of the spark plugs in an internal combustion engine. High tension leads, like many engine components, wear out over time. Each lead contains only one wire and allows the direct current from the distributor or coil to flow one way to the spark plug. The electrical circuit is completed through the earthed/grounded engine via the spark plug which is connected to the opposite battery terminal (negative terminal on modern engines).

What are they made from?

HT leads have an outer insulation made of a very flexible and heat-resistant material such as silicone or EPDM rubber. The thick insulation prevents arcing from the cable to an earthed engine component. A rubber “boot” covers each terminal.

If your vehicle has a running problem our technicians can carry out an initial basic check and test the resistance of a HT lead. From our workshop in the centre of Chatham in Medway our technicians can highlight any weakness and give you the correct diagnosis. Do not be surprised should your vehicle require HT leads then it is standard practice to replace the spark plugs at the same time. Quite often there will be visible signs that the spark has been tracking down the side of HT lead terminal leaving scorch marks on the side of the spark plug.

In modern systems the ignition or spark is electronically controlled by the ECU which is acting on information given from a cam or crank sensors, some of these modern systems do not have HT leads because the coils are placed directly on top of the spark plug (coil-on-plug or Direct Ignition).

A breakdown in a HT lead can result in a weak spark making the engine misfire and cause rough running. It could give bad fuel consumption or a loss of power. Total failure of a king lead can cause the vehicle not to start at all.

Why Choose Auto Experts Medway?

We at Auto Experts Medway in Medway have established a superb reputation for high quality vehicle repair services, refer to our testimonials from our customers from Chatham, Gillingham and Rochester on our testimonial page.

Auto Experts Medway in Chatham are near to both Rochester and Gillingham in the heart of Medway we are the local garage who can diagnose and fix all makes of vehicles.

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