Volvo 240/740/760/780/940/960 1990-1998

Spark Plug Wires



See Figures 1 and 2

Visually inspect the spark plug cables 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 wiring. If no physical damage is obvious, the wires can be checked with an ohmmeter for excessive resistance.

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.

  1. Remove the spark plug wires one at a time.
  3. Measure the length of the spark plug wire with a suitable tool. Write down the length.
  5. Connect one lead of an ohmmeter to one end of the spark plug wire on the metal conductor, and the other lead to the other end.
  7. Replace any wire which shows over 5,000-7,000 ohms per foot.

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


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 position). 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 successively shorter wire.