Mercury - Quicksilver 815407Q02 Distributor Cap Kit V6 GM MerCruiser Engines Thunderbolt IV & V HEI Ignition 815407Q02. Overview. When you turn the key and that V6 comes to life without a stumble, you can thank a good ignition system. The Quicksilver 815407Q02 Distributor Cap Kit helps keep it that way. Built for marinized GM-based MerCruiser engines with Thunderbolt IV or V HEI ignition, this genuine Mercury part keeps the spark clean and steady from idle to wide-open throttle.. It's made for t