Ford Mid-Size Cars 1971-1985 Repair Guide

Spark Plug Wires



See Figures 1 and 2

Visually inspect the spark plug cables (wires) for burns, cuts, or breaks in the insulation. Check the spark plug boots and the nipples on the distributor cap and coil. Replace any damaged spark plug wire in all types of ignition systems.

When installing a new set of spark plug cables (wires), replace the cables one at a time so there will be no confusion Start by replacing the longest cable first. Install the boot firmly over the spark plug. Route the cable exactly the same as the original. Insert the nipple firmly into the tower on the distributor cap. Repeat the process for each cable.

Whenever a spark plug wire is removed on a vehicle equipped with an Electronic Ignition System (EIS), silicone dielectric compound (grease) should be applied to the boot before it is reconnected. Using a small clean tool, coat the entire interior surface of the boot with Ford Silicone grease (D7AZ 19A331-A or equivalent).

Use an oscilloscope for testing and diagnosis. Do not puncture wires or use adapters as that can cause misfiring.

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Fig. Fig. 1: Using a spark plug wire removal tool will help prevent damage to the cables

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Fig. Fig. 2: Testing spark plug wire resistance with an ohmmeter

Duraspark Type Plug Wires

The spark plug wires used with the Duraspark type ignition system are 5 / 16 in. (8mm) in diameter to contain the higher output voltage. There are two types of wires used in this system, and some engines may have both types installed. It is important to properly identify the type of wire used for each cylinder before replacements are made.

Both types are blue in color and have silicone jacketing. The insulation material underneath the jacketing on some plug wires is a silicone layer separated by glass braid. The plug cable not incorporating the silicone layer is used where engine temperatures are cooler and are identified with the letter SE with black printing. The plug cables with the silicone insulation are used where high engine temperatures are present. These cables are identified with the letters SS with white printing.

Each spark plug cable, if original, is marked with the cylinder number, model year and date of cable manufacture (quarter and year). Service replacement wires will not have cylinder numbers, or manufacture date.

On any vehicle equipped with a catalytic converter, never allow the engine to run for more than 30 seconds with a spark plug wire disconnected. Unburned fuel in the cylinder may ignite in the converter as it is exhausted and damage the converter.


When removing spark plug wires, mark and tag the individual wires. Grasp, then slowly, twist the insulator back and forth on the spark plug to free the insulator. Do not pull on the wire directly as it may become separated from the connector inside the insulator. Special tools are available which can help ease plug wire removal, and prevent damage to a cable.

When installing a new set of spark plug wires, replace the wires one at a time so there will be no confusion. Start by replacing the longest wire first. Route the wire exactly the same as the original.

  1. Disconnect the negative battery cable.
  3. Grasp the wire by the rubber boot. Twist and pull the boot and wire from the spark plug. Never pull on the plug wire directly.
  5. Remove the necessary wire retainer clips and separators, then remove the spark plug wire.

To install:
  1. Apply a small amount of silicone dielectric compound D7AZ-19A331-A or equivalent, to the entire inside surface of the spark plug wire boots. This is extremely important on the Duraspark wires.
  3. Install the wire to the proper distributor cap or ignition coil terminal, making sure the boot is firmly seated.
  5. Route the wire through the necessary retainer clips and separators.
  7. Connect the spark plug wire to the spark plug.
  9. Connect the negative battery cable.