Mercury Marine Alternator 8M0064021 – Fits Mercury/Mercruiser 2.5L Outboards (Replaces 889955A03)
Mercury Marine Alternator 8M0064021 – Fits Mercury/Mercruiser 2.5L Outboards (Replaces 889955A03) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
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Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Mercury Marine Alternator 8M0064021 – Fits Mercury/Mercruiser 2.5L ...
Product Details
This aftermarket Mercury Marine Alternator 8M0064021 is a high-quality replacement for various Mercury outboard engines, particularly 2.5L models. It is engineered to serve as a reliable 12-volt, 50-amp alternator designed for marine environments.
It directly interchanges with several part numbers, including Mercury 889955A03, Delco 19020706, and Sierra 18-6454, among others. See the Part Number Matrix for a complete list of cross-references.
- Designed for direct-fit installation.
- Features an internal fan for cooling.
- Includes a multi-groove serpentine pulley and wire/plug connector.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket brands.
| Brand | Part Number | Superseded By |
|---|---|---|
| Mercury | 889955A03 | 8M0064021 |
| Mercury | 834832 | |
| Mercury | 881248T | |
| Mercury | 875285T1 | |
| Mercury | 889955T01 | |
| Mercury | 8M6000804 | |
| Delco | 8600515 | |
| Delco | 19020703 | |
| Delco | 19020706 | |
| Sierra | 18-6454 | |
| Protorque | PH300-0031 |
Engine & Model Compatibility
Confirm your engine model and year in the table below.
For Mercury/Mercruiser owners, ensure your model matches the listed specifications. This part is a common replacement for 2.5L outboards that originally used part number 889955A03.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Mercury | 2.5L Outboard | 889955A03 | Superseded by 8M0064021 |
Technical Specs
- Product Type
- Alternator
- Voltage
- 12 Volts
- Output
- 50 Amps
- Installation
- Direct replacement
- Mounting
- 2-inch mounting foot
- Features
- Internal fan, Multi-groove serpentine pulley, Wire/plug connector included
- Dimensions
- 20.5 x 19.0 x 18.0 cm
- Weight
- 3.6 kg (7.94 lbs)
What’s in the Box
- 1 x Alternator Assembly (8M0064021)
Installation Notes
- Disconnect the vessel's battery terminals to prevent electrical shorts.
- Loosen the serpentine belt tensioner and remove the belt from the alternator pulley.
- Unplug the wire harness connector and detach the main power cable from the old alternator.
- Remove the mounting bolts and carefully lift the old alternator out of the engine bay.
- Position the new alternator and loosely tighten the mounting bolts.
- Re-install the serpentine belt, ensuring it is correctly routed and tensioned.
- Tighten all mounting bolts to the manufacturer's specified torque.
- Reconnect the power cable and wire harness plug.
- Reconnect the battery terminals.
- Start the engine and verify the charging system is operating correctly.
Troubleshooting & FAQ
How do I know if this alternator fits my Mercury engine?
The best method is to match your old part number to one listed in our Part Number Matrix. This alternator is a confirmed fit for Mercury 2.5L Outboards that used part 889955A03, but it also cross-references with many other numbers. Always visually compare the photos and specifications to your existing part.
What are the signs of a failing alternator?
Common symptoms include dimming lights, a warning light on the dash, a weak or dead battery, strange noises from the engine (whining or grinding), or the smell of burning rubber or wires. Use a multimeter to check the battery voltage with the engine running; it should be >13.5 volts.
Is this a direct bolt-on replacement?
Yes, this unit is designed to be a direct-fit replacement. It includes the correct 2-inch mounting foot, serpentine pulley, and wire/plug connector for the applications listed, requiring no modification for installation.
Do I need to charge my battery after installing this new alternator?
If your battery was drained by the old alternator, it is highly recommended to fully charge it with a dedicated battery charger before starting the engine. A new alternator is designed to maintain a charged battery, not to recharge a deeply discharged one.
How can I tell if my old alternator has an internal or external fan?
An internal fan is not visible from the outside of the alternator casing. An external fan will have visible blades, typically at the front behind the pulley. This model features an internal fan.
What maintenance does this alternator require?
Marine alternators are generally maintenance-free. The most important factor for longevity is ensuring the serpentine belt is in good condition and properly tensioned. A loose or worn belt can cause the alternator to perform poorly and fail prematurely.
OEM vs. Aftermarket?
This listing is an aftermarket replacement (not OEM). It is built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, it is batch-inspected for consistency and reliability.
Shipping speed & cost
We ship worldwide quickly—typical transit is 5–15 days. Standard shipping is free; expedited options appear at checkout where available.
Warranty & returns
This product is covered by a 1-year warranty against manufacturing defects under normal use. If any issues arise, contact our support team with your order details. Returns are accepted within our standard window for items that are unused and in original condition. See our policy page or reach out for instructions.
Safety & Important Info
- Verify images and specifications against your original part before purchase. If anything differs—even if your model is listed as compatible—do not purchase.
- This is an aftermarket replacement component, not an OEM part.
- Professional installation is recommended for safety and performance.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
- Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
- Manufacturer-Direct Value — Fair pricing without compromising on materials or quality control.
Payment & Security
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