300-8M0077471 184-0003 Ignition Coil for Mercury Optimax EFI | JLM Marine

Ignition Coil for Mercury Optimax EFI – Fits Mercury 2-Stroke & 4-Stroke Outboard Motors

This aftermarket ignition coil is engineered for Mercury Optimax, Mercury EFI 2-Stroke, Mercury EFI 4-Stroke, and Mercury Racing engines ranging from 30 HP to 300 HP. It delivers reliable spark and performance across a wide range of applications, including recreational, Pro XS, and racing models.

Direct replacement for Mercury OEM part numbers 300-8M0077471, 184-0003, 300-879984T01, 339-879984A1, 339-879984T00, 879984T01, 8M00774714. Built to meet or exceed OEM specifications for dependable ignition across demanding marine conditions.

• Compatible with Mercury Optimax, EFI 2-Stroke, EFI 4-Stroke, and Racing series engines
• Direct-fit replacement – no modifications required
• Meets or exceeds OEM performance standards

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 × Ignition Coil

Installation Guide

1. Disconnect the battery negative terminal to ensure safe working conditions. Confirm that the engine is off and cool to the touch.
2. Locate the ignition coil on your Mercury outboard motor. Refer to your engine's service manual or parts diagram if needed.
3. Disconnect the electrical connectors from the old ignition coil. Note the wire positions or take a photo for reference during reassembly.
4. Remove the mounting bolts securing the old coil to the engine block. Keep the hardware for reinstallation unless new fasteners are provided.
5. Remove the old ignition coil from the engine bay. Inspect the mounting area and clean any debris or corrosion.
6. Position the new ignition coil in place, aligning the mounting holes with the engine block. Ensure proper orientation and seating.
7. Install and tighten the mounting bolts to the manufacturer's recommended torque specification. Do not overtighten to avoid cracking the coil housing.
8. Reconnect the electrical connectors to the new ignition coil, ensuring each wire is fully seated and secure. Double-check all connections against your reference photo.
9. Reconnect the battery negative terminal. Ensure all tools and materials are clear of the engine bay.
10. Start the engine and listen for smooth operation. Check for misfires, rough idle, or warning lights on the dashboard.
11. Perform a test run at low speed, then gradually increase throttle to verify proper ignition performance. Monitor engine temperature and RPM stability.
12. Inspect all connections after the test run to confirm there are no loose wires or vibration-related issues. Recheck mounting bolt torque if necessary.

Troubleshooting & FAQ

How do I confirm this ignition coil fits my Mercury engine?
Check the Compatible Engine Models table above for your engine's horsepower, stroke type, and series (Optimax, EFI, Pro XS, Racing). Cross-reference your existing coil's part number with the Part Number Cross-Reference table to ensure compatibility.

What are the signs that my ignition coil needs replacement?
Common symptoms include engine misfires, rough idling, difficulty starting, loss of power, poor fuel economy, and intermittent stalling. If you experience any of these issues, inspect the ignition coil for cracks, corrosion, or burnt connectors.

How often should I replace my ignition coil?
Ignition coils do not have a fixed service interval and are typically replaced only when they fail. Regular inspection during seasonal maintenance is recommended, especially if you operate in saltwater or harsh conditions.

Can I install this ignition coil myself, or do I need a professional?
If you have basic mechanical skills and tools, you can install this coil following the Installation Guide above. However, professional installation is recommended to ensure proper torque, electrical connections, and ignition timing verification.

What's the difference between this aftermarket coil and the OEM Mercury part?
This 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.

How fast do you ship and how much does it cost?
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.

What is your warranty and return policy?
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.