Mercury - Quicksilver Distributor Cap Kit For GM V8 MerCruiser Engines with Thunderbolt IV & V Systems 805759T1. Overview. When your engine starts hesitating, missing, or losing power, it's often the distributor cap showing its age. The Mercury Marine 805759T1 Quicksilver Distributor Cap Kit brings back the clean, consistent spark your V8 MerCruiser needs. Designed for marinized GM-built engines running Thunderbolt IV and V HEI ignition systems, this cap is built tough - molded from high-strengt