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Ignition leads are the black flexible cable that connects a coil to a spark plug. In some cases a distributor sits between them and in others the coil makes a direct connection to the spark plug. No need for an ignition lead. They carry an extremely high voltage and need to be well insulated so no arcing occurs. They live in an engine bay which is full of metal and highly conductive so this is an important point.
They have a range of different connectors on either end and normally come terminated ready to install. Most suit a particular vehicle application so even if they look the same, the length may vary.
Popular Questions Asked
Why do Ignition Leads fail?
Ignition Leads will wear out and fail over time. This is due to a number of factors like contaminants in the engine bay (oil, fuel, dirt), heat, vibration and the insulation degrading.
How do I know if I need to replace my Ignition Leads?
The easiest thing is to check for damage or cracking. If they show signs of this replace them. Check to see they are not loose by pushing down on them or pulling on them. Always hold them by the boot when doing this. If you pull on the wire you can damage them. You can take them off and using a multimeter check their resistance. The longer the cable the greater the resistance. I have used a timing light to check them.
Can I replace Ignition Leads myself?
Yes, you can. They are not difficult as long as you don't rip all the old ones out before working out where the new ones go. Sometimes it is best to replace them one at a time. Make sure you buy the correct ones for your vehicle and engine.