Mercury - Quicksilver 816761Q16 Spark Plug Wire Kit V6 MerCruiser Engines Thunderbolt IV Ignition 816761Q16. Overview. Smooth, reliable ignition is what keeps your boat running like it should. The Quicksilver 816761Q16 Spark Plug Wire Kit brings your V6 MerCruiser engine (1985-2003) back to that factory-fresh performance. Built for Thunderbolt IV ignition systems, this OEM wire set restores clean spark delivery, steady idle, and quick starts - everything you need for dependable days on the water