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, remove the distributor cap, leaving the wires attached. Connect one lead of an ohmmeter to an electrode within the cap; connect the other leak to the corresponding spark plug terminal (remove it from the plug for this test). Replace any wire which shows a resistance over 30,000 ohms. Test the high tension leak from the coil by connecting the ohmmeter between the center contact in the distributor cap and either of the primary terminals of the coil. If resistance is more than 25,000 ohms, remove the cable from the coil and check the resistance of the cable alone. Anything over 15,000 ohms is cause for replacement. It should be remembered that resistance is also a function of length; the longer the cable, then greater the resistance. Thus, if the cables on your vehicles are longer than the factory originals, resistance will be higher, and quite possibly outside these limits.
Wire length can therefore be used to determine appropriate resistance values:
REMOVAL & INSTALLATION
If all the wires must be disconnected from the spark plugs or from the distributor at the same time, be sure to tag the wires to assure proper reconnection.
When installing a new set of spark plug wires, replace the wires one at a time so there will be no mix-up. Start by replacing the longest cable first. Install the boot firmly over the spark plug. Route the wire exactly the same as the original. Connect the wire tower connector to the distributor. Repeat the process for each wire. Be sure to apply silicone dielectric compound to the spark plug wire boots and tower connectors prior to installation.