Mercury - Quicksilver 816761Q3 Spark Plug Wire Kit V8 GM MerCruiser (RH) Engines (305 & 350 CID) Thunderbolt IV Ignition 816761Q3. Overview. When your engine fires clean and smooth, you can feel the difference right away. The Quicksilver 816761Q3 Spark Plug Wire Kit brings that performance back to your V8 right-hand rotation MerCruiser engine (305 and 350 CID) equipped with Thunderbolt IV ignition systems (1981-1993).. This OEM kit includes a full set of plug wires built to factory specification