Mercury - Quicksilver 816608Q80 Red Wire Spark Plug Wire Kit MerCruiser 5.7L Inboard & Tow Sports Engines Thunderbolt IV Ignition 816608Q80. Overview. Good spark equals good power - and that starts with quality wires. The Quicksilver 816608Q80 Red Wire Spark Plug Wire Kit keeps your MerCruiser 5.7L inboard and tow-sports engine firing clean and strong. Designed for Thunderbolt IV ignition systems (1998-2010), this OEM wire set delivers reliable spark, clean combustion, and the kind of long-term