At every tune-up/inspection, visually check the spark plug cables for burns cuts, or breaks in the insulation. Check the boots and the nipples on the distributor cap and/or coil. Replace any damaged wiring.
Every 50,000 miles (80,000 Km) or 60 months, the resistance of the wires should be checked with an ohmmeter. Wires with excessive resistance will cause misfiring, and may make the engine difficult to start in damp weather.
To check resistance, disconnect the spark plug end and coil end of one spark plug wire. Connect an ohmmeter to lead to each end of the spark plug wire's terminals. A general rule is to replace the wire if the resistance is over 30,000 ohms. It should be remembered that resistance is a function of wire length and a longer wire may have more resistance. Today's vehicles are factory equipped with top quality spark plug wires since they must carry enormous amounts of energy, and, if treated carefully, generally give little trouble for the life of the vehicle.