Sierra 18-8810-1 Mercruiser Thunderbolt V6 Spark Plug Wire Set Sierra replacement spark plug wire set for Mercruiser Stern Drives. For 6 cylinder engines with Thunderbolt ignition systems. Kit includes coil wire. Kevlar core for maximum durability and long life. Durable stainless steel wound conductor for maximum horsepower and engine performance. Premium silicone jacketing and boots for the ultimate in high temperature protection. Superior RFI suppression for the most sensitive electronic syste