Sierra Spark Plug Wire Set 18-8821-1 for Mercruiser 260, 300, 320 EFI, 350 Mag Alpha Thunderbolt IV 8-Cylinder Engines

The Sierra 18-8821-1 Spark Plug Wire Set is a complete 8-cylinder ignition wiring kit built for Mercruiser stern drive engines equipped with a Thunderbolt IV distributor. The set includes eight spark plug wires plus a coil wire, all terminated with corrosion resistant stainless steel spark plug and distributor terminals for reliable conductivity in the marine environment. Spark plug wire lengths are (2) 29 inches, (2) 34 inches, (2) 38 inches, and (2) 44 inches, with a single 12 inch coil wire, giving the correct reach for routing around an 8-cylinder Mercruiser block without excess slack or strain on the terminals.

This wire set is engineered to meet or exceed the performance of the original equipment wiring it replaces, built to withstand heat, vibration, moisture, and salt exposure typical of marine ignition systems. It is designed as a direct fit for the Mercruiser 260, 260 MIE, 300, 320 EFI, and 350 Mag Alpha engines listed below, all of which use the Thunderbolt IV distributor on an 8-cylinder configuration.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-8821-1
• Material: Stainless Steel
• Number of Spark Plug Wires: 8
• Spark Plug Wire Lengths: (2) 29 inches, (2) 34 inches, (2) 38 inches, (2) 44 inches
• Coil Wire Length: 12 inches (1)
• Terminal Type: Corrosion resistant stainless steel spark plug and distributor terminals
• Distributor Type: Thunderbolt IV
• Engine Configuration: 8 Cylinder
• Item Dimensions: 10.25 x 7.25 x 2.75 inches
• Weight: 2 pounds
• UPC: 808282194499

Fitment

• Mercruiser 260, 8 Cylinder, Thunderbolt IV distributor, 1982 to 1987
• Mercruiser 260 MIE (LH), 8 Cylinder, Thunderbolt IV distributor, 1981 to 1986
• Mercruiser 260 MIE (RH), 8 Cylinder, Thunderbolt IV distributor, 1981 to 1986
• Mercruiser 300, 8 Cylinder, Thunderbolt IV distributor, 1985 to 1986
• Mercruiser 320 EFI, 8 Cylinder, Thunderbolt IV distributor, 1987 to 1989
• Mercruiser 350 Mag Alpha, 8 Cylinder, Thunderbolt IV distributor, 1986 to 1994

Frequently Asked Questions

What engines does the Sierra 18-8821-1 spark plug wire set fit? It fits Mercruiser 8-cylinder engines equipped with a Thunderbolt IV distributor, specifically the 260, 260 MIE (LH and RH), 300, 320 EFI, and 350 Mag Alpha models.

How many wires are included in this set? The 18-8821-1 set includes 8 spark plug wires plus 1 coil wire, enough for a complete 8-cylinder ignition wiring job.

What are the individual wire lengths? Spark plug wire lengths are (2) 29 inches, (2) 34 inches, (2) 38 inches, and (2) 44 inches, with a single 12 inch coil wire.

What material are the terminals made from? The 18-8821-1 set uses corrosion resistant stainless steel spark plug and distributor terminals for reliable conductivity in the marine environment.

Does this wire set work with a Thunderbolt IV distributor? Yes, the Sierra 18-8821-1 is specifically designed for Mercruiser engines using the Thunderbolt IV distributor.

Will this fit a Mercruiser 260 MIE with a serial number in the 5907058 to 0B788151 range? Yes, both the left-hand (LH) and right-hand (RH) 260 MIE Thunderbolt IV engines with serial numbers 5907058 through 0B788151 use the 18-8821-1 wire set.

What year range does this part cover for the Mercruiser 350 Mag Alpha? For the 350 Mag Alpha with Thunderbolt IV distributor, the 18-8821-1 covers 1986 to 1994.

Is this a genuine Sierra part or an aftermarket copy? The 18-8821-1 is a genuine Sierra part, manufactured to meet or exceed the original equipment part it replaces.

What is the weight of this spark plug wire set? The Sierra 18-8821-1 spark plug wire set weighs 2 pounds.

Does the 18-8821-1 fit the Mercruiser 320 EFI? Yes, it fits the Mercruiser 320 EFI with a Thunderbolt IV distributor, covering serial numbers 0A543604 to 0C622418 from 1987 to 1989.

Are the wires resistant to corrosion in a marine environment? Yes, the terminals on the 18-8821-1 set are corrosion resistant stainless steel, built to withstand the marine environment's heat, vibration, and moisture.

What is included with the 18-8821-1 kit? The kit includes the complete 8-cylinder spark plug wire set: 8 spark plug wires and 1 coil wire for a Mercruiser Thunderbolt IV ignition system.