How to Test and replace Spark Plug Wires on Ford?

The spark plug Testing and replacing procedure is as follows:---

Removal & Installation

  1. Label each spark plug wire and make a note of its routing.
    Don-t rely on wiring diagrams or sketches for spark plug wire routing. Improper arrangement of spark plug wires will induce voltage between wires, causing misfiring and surging. Be careful to arrange spark plug wires properly.
  2. Starting with the longest wire, disconnect the spark plug wire from the spark plug and then from the coil pack.
  3. Disconnect the ignition wire from the coil pack by squeezing the locking tabs and twisting while pulling upward. 

    Fig. Spark plug wire routing-3.0L engine

    Click image to see an enlarged view
    Fig. Spark plug wire routing-3.8L engine

    Click image to see an enlarged view
    Fig. Spark plug wires are attached to the coil pack with special clips. Squeeze the clips to disconnect the wire
To install:
  1. If replacing the spark plug wires, match the old wire with an appropriately sized wire in the new set.
  2. Lubricate the boots and terminals with dielectric grease and install the wire on the coil pack. Make sure the wire snaps into place.
  3. Route the wire in the exact path as the original and connect the wire to the spark plug.
  4. Repeat the process for each remaining wire, working from the longest wire to the shortest.


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 100,000 miles (160,000 km), 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.
  1. Disconnect the spark plug wire at the spark plug and the coil pack.
  2. Measure and note the length of the spark plug wire.
  3. Using a ohmmeter, measure the resistance between the spark plug wire terminals.
  4. Resistance should be less than 7000 ohms per foot of spark plug wire.
    If one spark plug wire is found to be out of specification, it is a good idea to replace the entire set.
  5. If resistance is excessive, the spark plug wire is faulty.

    Click image to see an enlarged view
    Fig. Checking individual plug wire resistance with a digital ohmmeter

This details will help.


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