Mercury - Quicksilver 816608Q61 Red Wire Spark Plug Wire Kit GM V8 Marine Engines (454-502 CID) Thunderbolt IV & V Ignition 816608Q61. Overview. The right spark plug wires can bring an older engine back to life. The Quicksilver 816608Q61 Red Wire Spark Plug Wire Kit is designed for vintage V8 GM-based MerCruiser engines (454-502 CID) using Thunderbolt IV and V ignition systems (1981-1997). Built to Mercury's standards, this OEM set keeps your ignition system firing clean and strong, restoring sm