Mercury – Spark Plug Wires | V12 Verado & SeaPro Series | Marine-Grade | 8M0178258

Overview

When you run a big outboard — especially a V12 — you get used to relying on parts that just work. Spark plug wires might not be the first thing you think about when you push the throttles forward, but you definitely feel their influence every time the engine lights off clean, smooth, and strong. The Mercury 8M0178258 Spark Plug Wires are built with that exact kind of trust in mind. They give you the comfort of knowing every cylinder is firing exactly when it should, whether you’re idling through a quiet marina at sunrise or pushing offshore with a heavy load and a long run ahead.

Key Features

• Delivers dependable spark distribution to all twelve cylinders
• Marine-grade construction built to withstand heat, vibration, and moisture
• Complete replacement set with twelve spark plug wires
• Designed specifically for Mercury V12 ignition timing and coil placement
• Durable insulation resists breakdown from engine compartment temperatures

Engine & Boat Compatibility

These Mercury Marine spark plug wires are engineered for:

• Mercury 7.6L V12 600hp Verado outboards
• Mercury 7.6L V12 500hp SeaPro outboards

Ideal for a wide range of larger vessels, including:

• Offshore center consoles
• Commercial and patrol boats
• Big multi-engine fishing rigs
• High-performance cruising platforms

If your boat relies on V12 power, these wires are designed with your setup in mind.

Performance & Practical Benefits

A V12 demands precision. With twelve cylinders firing in tight rhythm, the ignition system can’t afford even a slight misfire. These spark plug wires help maintain a steady, confident pulse throughout the entire powerband. You’ll notice the difference in how smoothly the engine starts, how evenly it idles, and how it pulls without hesitation when you roll into the throttles.

Mercury builds these wires to handle the harsh realities of marine life — constant vibration, pounding chop, and a hot engine compartment that never completely cools off after shutdown. The insulation stays flexible, the ends stay tight, and the spark stays consistent. That reliability translates directly to better fuel efficiency, cleaner burns, and fewer surprises when you’re miles from the nearest dock.

And the best part? Installation is straightforward. Each wire is the correct length, with the correct boots, so you’ll get that clean, factory fit without having to wrestle anything into place.

Why Buy OEM

With something as critical as ignition, cutting corners isn’t worth the risk. Mercury’s spark plug wires go through torture-testing designed for marine extremes — not just general automotive use. That means:

• Proper resistance and conductivity for V12 timing requirements
• Confidence that each cylinder receives a consistent spark
• Long-term durability in salt, heat, and constant motion
• No compatibility guesswork or premature failures
• The same performance Mercury intended when they engineered the engine

OEM equals peace of mind, plain and simple.

FAQ

Q1: Which engines does this set fit?

These spark plug wires fit Mercury 7.6L V12 600hp Verado and 500hp SeaPro outboards.

Q2: How are these different from aftermarket wires?

They’re built specifically for marine V12 demands — correct lengths, proper resistance, and materials tested for hot, wet engine compartments.

Q3: How do I know this is the right replacement?

Match the part number and your engine model. If you’re running a Mercury V12, this set is designed for your powerplant.

Q4: Are these safe for both freshwater and saltwater applications?

Absolutely. The insulation and connectors are designed to resist corrosion and moisture in all environments.

Q5: Can most boat owners install them themselves?

Yes. The wires are plug-and-play and install using basic tools. Just replace each wire one at a time to maintain correct routing.