Ignition Leads: High-Voltage Cables for Distributor and Coil-Pack Engines

Ignition leads (also called HT leads or plug leads) carry the high-voltage pulse from coil or distributor to each spark plug. They’re only fitted to engines with distributor-based ignition or coil-pack designs where the coils aren’t mounted directly on the plugs. Coil-on-plug engines don’t have leads.

How they fail

The high-voltage insulation degrades over years of heat and engine-bay exposure. Eventually the insulation breaks down and the spark arcs to ground (engine block, exhaust manifold) rather than the plug. Symptoms: misfire (especially in damp weather), reduced power, visible blue arc on the leads at night when the engine is running.

Suppressor failure (internal resistor inside the lead) causes intermittent open-circuit. Fault codes for misfire on specific cylinders.

Replacement

Replace as a set — leads on the same engine age together. Note the routing carefully before removal; some engines have specific anti-crosstalk routing requirements.

Brand

NGK, Bosch, Beru cover OE-equivalent leads. Magnecor and BBP for performance applications.

Find ignition leads for your engine on the Ignition Leads collection.