Spark plug wires in an MX5 NB (1998–2000) carry high ignition voltage from the ignition coil to the spark plug, precisely at the moment the fuel-air mixture in the cylinder needs to ignite. Where heat, vibrations, and age come together, you often see the wire insulation harden or internal resistance slowly increase, causing the spark to lose some of its power. You’ll notice this in the engine’s idle, throttle response, or an engine that doesn’t accelerate as smoothly under load. As long as the rest of the ignition system—including spark plugs and sensors —is functioning properly, combustion remains stable.
