Mercury - Gray Spark Plug Wire/Lead Ignition System Component Durable Marine-Grade Construction 857124A1. OverviewEvery boater knows that a smooth-running engine starts long before the key turns-it begins with a clean, strong spark. When you're heading out before sunrise or easing back toward the dock at the end of a long day, you want to trust that your ignition system won't miss a beat. That's why a dependable spark plug wire matters more than most folks realize. The Mercury Marine part number