Spark Plug Wire Set – Fits Mercruiser 4-Cylinder 2.5L/3.0L (Replaces 816761A5, 84-816761Q5)

Spark Plug Wire Set – Fits Mercruiser 4-Cylinder 2.5L/3.0L

This spark plug wire set is designed for Mercruiser 4-cylinder engines with model designations 120, 140, 2.5L (153 CID), and 3.0L (181 CID) GM sterndrive motors using conventional points ignition systems from 1963-1995.

It serves as a direct replacement for multiple OEM and aftermarket part numbers, ensuring a precise fit and reliable performance for your marine engine.

• Compatible with gasoline engines.
• Engineered for a direct replacement installation.
• Includes a complete set of wires with pre-installed spark plug boots.

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

Confirm your engine model/year in the table below. For Mercury owners, here’s a guide to help you identify your engine’s serial/model: Mercury Serial Number Guide. You can also review exploded diagrams to verify part numbers: Mercury Parts Diagrams & Catalog.

Technical Specifications

Package Contents

• 1 x Complete Spark Plug Wire Set with Boots (816761A5)

Installation Guide

1. Safety First: Before you begin, disconnect the boat's battery to prevent any electrical accidents.
2. One by One: Replace one spark plug wire at a time to avoid mixing up the firing order. This is critical for engine timing.
3. Remove the Old Wire: Firmly grasp the boot at the spark plug and twist slightly to break the seal, then pull it straight off. Do the same at the distributor cap end.
4. Match the Length: Compare the new wire with the old one to ensure it's the correct length for that specific cylinder.
5. Apply Dielectric Grease: Apply a small amount of dielectric grease to the inside of both boots of the new wire. This prevents corrosion and makes future removal easier.
6. Install the New Wire: Push the new wire's boot firmly onto the spark plug until you feel it click into place. Repeat for the distributor cap end.
7. Repeat Process: Continue this process for the remaining cylinders.
8. Final Check: Once all wires are replaced, ensure they are routed correctly and away from hot or moving engine parts. Reconnect the battery.

Troubleshooting & FAQ

Q: How do I confirm this wire set fits my specific engine?
A: Please check the "Compatible Engine Models" table on this page. Verify your engine model, year, and serial number range. Cross-referencing your old part number with our "Part Number Cross-Reference" table is the best way to guarantee a match.

Q: What are common signs that my spark plug wires need replacing?
A: Worn spark plug wires can cause engine misfires, a rough idle, poor acceleration, and decreased fuel economy. Visible signs include cracked insulation, corrosion on the connectors, or burn marks.

Q: Is this a complete set for my engine?
A: Yes, this is a complete set containing all the necessary ignition wires for the specified 4-cylinder Mercruiser engines.

Q: OEM vs. Aftermarket?
A: This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

Q: How fast do you ship and how much does it cost?
A: We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

Q: What is your warranty and return policy?
A: This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.