Ignition lead tips

Practical advice on using ignition leads: never touch them with the engine running, remove them only when the engine is cold and never pull on the lead itself. Fit the boots carefully so that they click into place, replace the complete set rather than single leads, and renew ignition leads every 50,000 km or every 3 years.

To keep your car running smoothly, here are some practical tips on using ignition leads.

How to get the best from your ignition leads

• Do not touch the leads while the engine is running! You could get an electric shock. Remove the leads only when the engine is cold, so that you do not tear the metal terminal off the lead. Never pull on the lead itself!
• Take particular care when fitting the leads to the distributor cap and the ignition coil. The rubber boots, which seal the connection, trap air when they are pushed on. With the engine running, this air heats up and the boots can "pop off like champagne corks", breaking the electrical connection.
• After replacing or cleaning the spark plugs, make sure the leads are refitted correctly. When fitted properly, the metal terminal noticeably snaps into place with a sound similar to a press stud closing.
• Incorrect fitting on the spark plugs, distributor cap or coil makes the spark jump (arc over), which burns a hole through the rubber insulator.
• Leads that glow or spark in the dark have not necessarily suffered insulation breakdown or stopped working properly. Their specific construction strongly ionises the surrounding air, causing external electrical discharges. These discharges will not give you an electric shock.
• Replace the complete set, not single leads. Use single leads only in an emergency. According to statistics, failed high-voltage leads are the most common reason for roadside assistance call-outs in Western Europe.
• Replace ignition leads every 50,000 km or every 3 years.