339-7452A19 339-7452A1 Switch Box CDI for Mercury Mariner | JLM Marine

Switch Box CDI for Mercury Mariner – Fits 6-35 HP 2-Stroke Outboards

This aftermarket CDI switch box is designed for Mercury Mariner 2-stroke outboard engines ranging from 6 HP to 35 HP. It provides reliable ignition control for two-cylinder models from 1980 to 1997 and newer 6-25 HP models from 1999 onward, ensuring consistent spark delivery and engine performance across a wide range of applications.

This unit directly replaces multiple Mercury/Quicksilver OEM part numbers including 339-7452A1, 339-7452A19, 339-7452A15, 339-7452A17, and many others, as well as Sierra 18-5777. It is compatible with engines using the bullet connection pack.

• Fits 6, 8, 9.9, 10, 15, 20, 25, and 35 HP Mercury Mariner 2-stroke engines
• Compatible with 1980-1997 models using bullet connection pack and 1999+ two-cylinder models
• Direct replacement for 339-7452A series and Sierra 18-5777

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

This package includes:

• 1 × CDI Switch Box Unit

Installation Guide

1. Disconnect the battery: Remove the negative terminal from the battery to ensure safety during installation.
2. Locate the old CDI switch box: It is typically mounted near the engine block or under the cowling.
3. Disconnect the wiring harness: Carefully pull apart the bullet connectors from the old CDI unit, noting the wire positions.
4. Remove mounting hardware: Unscrew or unbolt the old CDI switch box from its mounting location.
5. Position the new CDI unit: Place the new switch box in the same location as the old unit.
6. Secure the new unit: Use the original mounting screws or bolts to firmly attach the CDI box.
7. Reconnect the wiring harness: Attach each bullet connector to the corresponding terminal on the new CDI unit, ensuring a secure fit.
8. Verify all connections: Double-check that all wires are properly connected and no terminals are exposed.
9. Reconnect the battery: Attach the negative terminal back to the battery.
10. Test the ignition system: Turn the key to the "on" position and attempt to start the engine to verify proper operation.

Troubleshooting & FAQ

Q: How do I confirm this CDI switch box fits my Mercury engine?
A: Check the compatibility table above for your engine's horsepower, year, and stroke type. You can also verify the OEM part number stamped on your existing CDI unit against the cross-reference table to ensure a match.

Q: What are the signs that my CDI switch box is failing?
A: Common symptoms include difficulty starting the engine, misfiring, loss of power at high RPM, irregular idling, or complete failure to start. If you experience these issues after ruling out spark plugs and fuel delivery problems, the CDI may need replacement.

Q: Will this work with engines that have a different connector type?
A: This CDI is designed specifically for engines using the bullet connection pack. If your engine uses a different connector style, this unit may not be compatible without modification or an adapter harness.

Q: How often should I replace the CDI switch box?
A: CDI units typically do not require routine replacement and should last many years under normal operating conditions. Replace the CDI only when it shows signs of failure or after exposure to water damage, corrosion, or electrical surges.

Q: Is this an OEM part or 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.