CHECKING AND REPLACEMENT
At every tune-up, visually inspect the spark plug cables for burns, cuts, or breaks in the insulation. Check the boots and the nipples on the distributor cap and coil. Replace any damaged wiring. Every 36,000 miles (58,000 km) or so, 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. Generally, the useful life of the cables is 36,000-50,000 miles (58,000-80,000 km).
It should be remembered that resistance is also a function of length; the longer the cable, the greater the resistance. Thus, if the cables on your car are longer than the factory originals, resistance will be higher, quite possibly outside these limits.
When installing new cables, always replace them one at a time to avoid mix-ups. Start by replacing the longest one first. Install the boot firmly over the spark plug. Route the wire over the same path as the original. Insert the nipple firmly into the tower on the cap or the coil.