Mercury – Cap and Rotor Kit | For GM V8 MerCruiser Engines with Thunderbolt IV & V Systems | 805759T3Mercury Cap and Rotor Kit For GM V8 MerCruiser Engines with Thunderbolt IV & V Systems 805759T3 Overview A strong, reliable spark is the backbone of every good running engine. The Mercury Marine 805759T3 Cap and Rotor Kit restores smooth ignition performance to your GM based V8 MerCruiser equipped with Thunderbolt IV or V HEI ignition systems. Built with durable marine grade materials, this kit is designed to handle the heat, vibration, and humidity