Mercury - Quicksilver 816761Q17 Spark Plug Wire Kit V8 GM MerCruiser (LH) Engines (305 & 350 CID) Thunderbolt IV Ignition 816761Q17. Overview. Your engine's spark system is its heartbeat - and strong, steady spark is key to dependable power. The Quicksilver 816761Q17 Spark Plug Wire Kit keeps that spark strong in V8 left-hand rotation MerCruiser engines (305 and 350 CID) equipped with Thunderbolt IV ignition systems (1993-2003).. This OEM kit is built for the realities of boating: salt air, vibr