Have you ever watched your Mustang's ignition system in the dark with the engine running? Because ignition systems produce 20,000 to 50,000 volts of high-energy electricity, a certain amount escapes all the time, resulting in a light show under the hood at night. When spark plug wires get close to each other and close to ground, there's arcing you cannot see in daylight. The stray voltage isn't enough to cause misfires, but sacrifices are made in terms of spark intensity. When you lose current to ground or to another spark plug wire, you're not getting a potent spark at the cylinder on compression/ignition stroke.
Made 4 You Products understands the temperamental nature of ignition systems and high-voltage electricity. It also understands what looks good. That's why Made 4 You conceived Smoothie spark plug wire separator kits for 7-8mm ignition wire sets. These kits keep spark plug wires separated and uniformly rooted while maintaining a neat, clean appearance. They're priced right at $52.95 for a basic V-8 set.