Ford 5U2Z-12259-BA Cable Set

The spark plug wires should be checked at recommended intervals, or when replacing spark plugs. To do this, observe the spark plug wires while the engine runs. Start the engine in a darkened garage or at night and look at each plug wire. When a break has occurred in the wire, you will see arcing or a small blue spark coming from the broken area. At higher engine speeds, secondary ignition voltage increases; however, a faulty lead may not produce an arc at idle speed. As mentioned earlier, examine the wires for any indications of arcing. Replace all spark plug wires if arcing is observed.