Chevrolet Blazer/Jimmy 1969-1982 Repair Guide

Spark Plug Wires



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Fig. Fig. 1 Spark plug wire routing-6-cylinder HEI system

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Fig. Fig. 2 Spark plug wire routing-V8 HEI system

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Fig. Fig. 3 Inspect the distributor cap and rotor for damage and carbon tracking. Clean or replace if either component is dirty or defective

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Fig. Fig. 4 Checking plug wire resistance through the distributor cap with an ohmmeter

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Fig. Fig. 5 Checking individual plug wire resistance with a digital ohmmeter

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 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:

  1. Remove the distributor cap, leaving the wires in place.
  3. Connect one lead of an ohmmeter to an electrode within the cap.
  5. Connect the other lead to the corresponding spark plug terminal (remove it from the spark plug for this test).
  7. Replace any wire which shows a resistance over 30,000 ohms. Generally speaking, however, resistance should not be over 25,000 ohms, and 30,000 ohms 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 truck are longer than the factory originals, the resistance will be higher, possibly outisde these limits.


When installing new wires, replace them one at a time to avoid mixups. Start by replacing the longest one first.

  1. Remove the spark plug wire by gripping the boot firmly and disengaging the wire from the spark plug and the distributor.
  3. Install the boot of the new wire firmly over the spark plug. Route the wire over the same path as the original.