CDI Unit / Power Pack / Switch Box for Mercury & Mariner Outboards

High-quality marine-grade aftermarket CDI ignition unit / power pack / switch box for selected Mercury and Mariner 6 HP, 8 HP, 9.9 HP, 10 HP, 15 HP, 20 HP and 25 HP 2-stroke outboard engines.

Designed for selected:

2 Cylinder – 2 Stroke – 4 Magnet Flywheel

Mercury / Mariner outboards manufactured approximately 1997–2006, depending on the exact horsepower, model and serial number.

Designed as a replacement for:

855713A3 / 855713A4

Fits Selected Mercury / Mariner Outboards

6 HP

Selected:

2 Stroke
2 Cylinder
4 Magnet Flywheel
Approx. 1997–2005

8 HP

Selected:

2 Stroke
2 Cylinder
4 Magnet Flywheel
Approx. 1997–2005

9.9 HP

Selected:

2 Stroke
2 Cylinder
4 Magnet Flywheel
Approx. 1997–2005

10 HP

Selected:

2 Stroke
2 Cylinder
4 Magnet Flywheel
Approx. 1997–2005

Including selected:

10 HP
Sea Pro
Marathon

applications depending on serial number and specification.

15 HP

Selected:

2 Stroke
2 Cylinder
4 Magnet Flywheel
Approx. 1997–2006

Including selected standard and commercial applications depending on serial number.

20 HP

Selected:

2 Stroke
2 Cylinder
4 Magnet Flywheel
Approx. 1998–2006

Including selected standard and commercial applications.

25 HP

Selected:

2 Stroke
2 Cylinder
4 Magnet Flywheel
Approx. 1998–2006

Including selected:

25 HP
25 XD
Sea Pro / Marathon applications

depending on exact engine specification.

Fitment Summary

HP	Engine	Cylinders	Approx. Application
6 HP	2 Stroke	2	1997–2005
8 HP	2 Stroke	2	1997–2005
9.9 HP	2 Stroke	2	1997–2005
10 HP	2 Stroke	2	1997–2005
15 HP	2 Stroke	2	1997–2006
20 HP	2 Stroke	2	1998–2006
25 HP	2 Stroke	2	1998–2006

Selected applications use a:

4 MAGNET FLYWHEEL

⚠️ IMPORTANT

The year ranges are a guide only.

Do NOT assume every Mercury / Mariner 6–25 HP engine manufactured during these years uses this CDI.

Replaces Mercury / Mariner Part Numbers

855713A3
855713A4

Also searchable as:

855713-A3
855713-A4
855713 A3
855713 A4
855713

Additional Cross References

CDI Electronics 114-5713
CDI 1145713
Sierra 18-99222

OEM manufacturer names and part numbers are provided for identification and compatibility reference only.

⚠️ VERY IMPORTANT – 4 MAGNET FLYWHEEL

This CDI / switch box is designed for selected 1997–2006 Mercury / Mariner 2-cylinder 2-stroke engines using a 4-magnet flywheel ignition system.

Please check your engine before ordering.

Do not select the CDI simply because your engine is:

6 HP
8 HP
9.9 HP
10 HP
15 HP
20 HP
25 HP

Mercury / Mariner used different ignition systems across these horsepower ranges.

⚠️ IMPORTANT – Check Your Existing CDI

Before ordering, compare your existing CDI / switch box carefully.

Check:

Original part number
Electrical plugs / connections
Wiring configuration
Number of cylinders
Flywheel / ignition system
Complete engine serial number
Mounting arrangement

Ideally, your original switch box should cross-reference to:

855713A3 or 855713A4

Different From Earlier 339-7452A CDI

Mercury / Mariner used a different CDI / switch-box family on many earlier 6–25 HP 2-cylinder engines.

Earlier Engines – Approx. 1980–1997

Common switch-box family:

339-7452A19 / 339-7452A15

Later Engines – Approx. 1997–2006

This listing:

855713A3 / 855713A4

These CDI units are NOT interchangeable simply because the horsepower is the same.

Always identify the ignition system and original part number before ordering.

What Is a CDI / Switch Box?

The CDI / switch box is an important component of the Mercury / Mariner ignition system.

It receives electrical signals from the ignition system and controls the electrical output used to fire the ignition coils.

A faulty CDI / switch box can be associated with symptoms such as:

No spark
Intermittent spark
Loss of spark on one cylinder
Difficult starting
Misfiring
Engine cutting out
Loss of ignition when hot
Irregular engine operation

Important

These symptoms do not automatically mean the CDI is faulty.

Similar problems can be caused by the stator, trigger, ignition coils, stop circuit, wiring or poor electrical connections.

Proper diagnosis is recommended before replacing the CDI.

Product Features

Marine-grade aftermarket CDI unit
CDI ignition module
Power pack
Switch box
Suitable for selected Mercury outboards
Suitable for selected Mariner outboards
6 HP
8 HP
9.9 HP
10 HP
15 HP
20 HP
25 HP
2 Stroke
2 Cylinder / Twin Cylinder
Selected 4-magnet flywheel applications
Approx. 1997–2006
Replacement for 855713A3
Replacement for 855713A4
Cross-reference CDI 114-5713
Direct replacement for compatible applications
New aftermarket ignition component

⚠️ Appearance Does Not Confirm Fitment

If the CDI looks the same as the one fitted to your engine, this does not always mean it is the correct part for your outboard.

Different Mercury / Mariner CDI units can look very similar but have different:

Internal specifications
Wire connections
Ignition-system requirements
Applications

Please check the original part number and complete engine details before purchasing.

Before Replacing Your CDI / Switch Box

If your engine has an ignition fault, we recommend checking the complete ignition system before installing a replacement CDI.

Check:

Stator output
Trigger output
Ignition coils
Spark plugs
Spark plug leads
Stop / kill circuit
Engine earth / ground connections
CDI wiring
Electrical plugs and connectors
Burnt or corroded terminals
Damaged or melted wiring

A fault elsewhere in the ignition system can produce symptoms similar to a failed CDI and may damage a replacement component.

Aftermarket Replacement Part

This is a high-quality marine-grade aftermarket replacement part.

It is not a genuine Mercury, Mariner or Quicksilver component.

OEM manufacturer names and part numbers are provided for identification and compatibility reference only.

The component is designed as a replacement for compatible Mercury / Mariner applications using:

855713A3 / 855713A4

What's Included

1 × CDI Unit / Power Pack / Switch Box

New aftermarket replacement component.

Buyer Responsibility

It is the buyer's responsibility to confirm compatibility before purchasing.

Please check:

Engine horsepower
2-stroke engine
2-cylinder configuration
Complete engine serial number
Original CDI part number
Electrical connections
4-magnet flywheel application where applicable

If you are unsure, please send SSI Marine:

Engine horsepower + complete serial number + clear picture of your existing CDI and connections

Our technical team will be happy to help identify the correct ignition unit.

Why Buy From SSI Marine?

Marine-grade aftermarket & OEM-spec parts
Workshop-tested products
More than 10 years supplying and working with outboard engines
Same-day dispatch before 1 PM Monday–Friday
Royal Mail Tracked 24
UK stock
Collection available from Leigh, Greater Manchester
Technical support from experienced outboard specialists
Workshop open Monday–Friday, 9 AM–5 PM

6 HP 8 HP 9.9 HP 10 HP 15 HP 20 HP 25 HP Mercury Mariner Outboard 2 Stroke CDI Switch Box 855713A4