Little by little, you have perceived a difference in your gas mileage, engine power and smoothness of your ride - and you suspect your Plymouth spark plug wires are to blame. After all, your Plymouth spark plug wires are a key component to maintaining the combustion cycle. What happens during a misfiring? Spark plug wires are designed to carry the electrical voltage from the ignition system to the spark plug. They are designed to have very low resistance against the current passing through the system, which allows the maximum amount of energy to be transferred. When that transfer of energy is interrupted, the spark that begins the combustion cycle will not ignite. A misfire or a poor spark will curtail your engine from reaching its peak power and efficiency. When you inspect your wires, first look for signs of arcing, which means that the spark is leaking out and jumping to a nearby ground somewhere in the engine. Run the engine in darkness, and watch the engine for the sight of little electrical arcs. Listen for the snap-crack of electricity. Spray the plug wire ends with clean water while you run the engine at idle during this test. Or, take a jumper wire and ground the metal part of the screwdriver. Warning: take care to choose one with a well-insulated handle. Touch the tip of the screwdriver to the wire, and around the coil and boots. If you see an electrical show, it's time to replace your Plymouth spark plugs.