Mercury - Quicksilver 815407A2 Distributor Cap Kit V6 GM MerCruiser Engines Thunderbolt IV & V HEI Ignition 815407A2. Overview. When your boat fires up instantly and idles smooth, that's your ignition system doing its job - and the Quicksilver 815407A2 Distributor Cap Kit helps keep it that way. Built for marinized V6 MerCruiser engines made by GM using Thunderbolt IV and V HEI ignition systems, this OEM cap delivers the clean, steady spark your engine depends on.. It's made from durable, heat-r