Mercury - Spark Plug Wire Kit Ignition System Marine-Grade Construction 863656A03. Overview. There is something reassuring about turning the key and hearing your engine fire cleanly on the first crank. When you spend your weekends around tow boats, wake boats, and other vessels built to haul friends and gear across the water, you learn quickly that ignition quality is everything. A good set of spark plug wires does more than carry current-they set the tone for every ride. This Mercury Marine par