Ford Mustang 1989-1993 Repair Guide

Spark Plug Wires



See Figures 1 and 2

Click image to see an enlarged view

Fig. Fig. 1: Checking plug wire resistance through the distributor cap with an ohmmeter

Click image to see an enlarged view

Fig. Fig. 2: 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. Start by wiping the wires with a clean, damp cloth. The carefully inspect the surface of the wires. Check the boots and the nipples on the distributor cap and/or ignition coil (as applicable). 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 on the distributorless 2.3L (VIN M) engine, remove a wire from the both the spark plug and the ignition coil pack tower, then use an ohmmeter probe at each end. On the 2.3L (VIN A) and on 5.0L engines, remove the distributor cap, then unplug only 1 wire at a time from the spark plug. Check resistance from the inside terminal of the distributor cap to the spark plug end of the cable. In both cases, resistance of any given spark plug wire should be LESS than 7000 ohms per foot of wire. Therefore a 2 foot long spark plug wire with 10,000 ohms of resistance would be acceptable (less than the 14,000 ohm max.), while the same wire should be discarded if resistance is 15,000 ohms.

If all of the wires must be disconnected from the spark plugs, coil packs or distributor cap at one time, be sure to tag the wires to assure proper installation.

The best possible method for installing a new set of wires is to replace ONE AT A TIME so there can be no mix-up. On distributor equipped engines, don't rely on wiring diagrams or sketches, since the position of the distributor can be changed (unless the distributor is keyed for installation in only one direction). Start by replacing the longest wire first. Install the boot firmly over the spark plug. Route the wire in exactly the same path as the original and connect it to the distributor or coil pack (as applicable). Repeat the process for each shorter wire.