Chevrolet Full-size Cars 1968-1978 Repair Guide

Spark Plug Wires



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Fig. Fig. 1 If HEI equipped, disconnect the retainer, then remove the plug wire from the retainer

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Fig. Fig. 2 Replace the wires one at a time and follow the original path of the wire

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Fig. Fig. 3 Checking plug wire resistance through the distributor cap with an ohmmeter

Every 15,000 miles, inspect the spark plug wires for burns, cuts, or breaks in the insulation. Check the boots and the nipples on the distributor cap. Replace any damaged wiring.

Every 45,000 miles 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 45,000-60,000 miles.

To check resistance, remove the distributor cap, leaving the wires in place. Connect one lead of an ohmmeter to an electrode within the cap; connect the other lead to the corresponding spark plug terminal (remove it from the spark plug for this test). Replace any wire which shows a resistance over 30,000 omega . Generally speaking, resistance should not be over 25,000 omega , and 30,000 omega must be considered the outer limit of acceptability.

It should be remembered that resistance is also a function of length; the longer the wire, the greater the resistance. Thus, if the wires on your car are longer than the factory originals, resistance will be higher, quite possibly outside these limits.

When installing new wires, replace them one at a time to avoid mixups. 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 onto the tower on the distributor cap, then install the cap cover and latches to secure the wires.