Mercury - Spark Plug Wire Kit Ignition System Marine-Grade Construction 863656A2. Overview. There is something reassuring about turning the key and hearing your engine catch instantly, settling into that smooth, familiar rhythm you trust. When your ignition system is dialed in, the whole boat feels more alive-responsive, steady, and ready for whatever kind of day you have planned on the water. That is the kind of confidence this Mercury Marine spark plug wire kit brings back to your 4.3L engine.