ROTA0721 Alternator for 2.5L Mercruiser Model 120 1987-1989 A000B0331
ROTA0721 Alternator for 2.5L Mercruiser Model 120 1987-1989 A000B0331

ROTA0721 Alternator for 2.5L Mercruiser Model 120 1987-1989 A000B0331

Item #: 400-46002

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DB Electrical alternators are highly engineered for excellence in performance.
  • Built to Beat the Heat: High temperature epoxy and high temperature grease withstand extreme heat
  • Heavy-duty rectifiers and high-quality regulators enhance superior charging performance
  • Most alternators are supplied with final test results and performance curve
  • Direct-fit replacement and easy installation made possible with OEM fitment specifications
  • Factory direct, money-saving alternator typically priced substantially less than OEM counterparts
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  • Product Info
  • Applications List
  • Part Replacement List
  • Policy Information
  • Reviews

Overview

DB Electrical Alternators
DB Electrical keeps vehicles of every shape and size moving forward – from mowers, motorcycles and ATVs to automobiles, tractors, pickups and large commercial trucks. We work directly with factories to ensure each component is manufactured to our exacting quality control standards. But because there is no middleman, we can offer these exceptional-quality electrical components at low factory direct prices.

With DB Electrical alternators, you’ll get …

  • Superior Quality Every Time – Our aftermarket alternators deliver performance that’s equivalent to the original.
  • Direct-Fit OEM Replacement Parts – DB Electrical aftermarket alternators are designed for perfect fitment to replace the ones that originally came with your vehicle.
  • Engineer-Tested Excellence – Our alternators go through a rigorous testing program to ensure optimal performance. Most alternators are supplied with their final test results and performance curve.

Reasons to choose DB Electrical for your next alternator:

  • Built to Take the Heat – Most DB Electrical alternators offer high-temperature epoxy, heavy-duty rectifiers, high-quality regulators, top-quality bearings and high-temperature grease for better charging and longer life under high-heat environments.
  • Depth of Inventory – Find both common and hard-to-find alternators for virtually any type of vehicle to travel over road, trail or water.
  • Brand New Alternator – Never settle for a secondhand one. Many places will try to sell you a used alternator for about the price we’ll sell you a new one.

The DB Electrical Advantage – 1-Year Warranty
DB Electrical delivers exceptional value for products that we stand behind with our total-confidence 1-year warranty. Yes, you have a full year to make sure your alternator meets your expectations.

Item Number: ROTA0721

100% Brand New Aftermarket Part From DB Electrical

Product Specs

Item ConditionAftermarket Part
Unit TypeAlternator
Amperage55
Fan TypeExternal
Pulley TypeSolid
RegulatorInternal
Voltage12

Applications List

Select Make & Type
MAKE TYPE MODEL YEAR ENGINE
MercruiserEngineModel 2301981-955
MercruiserEngineModel 26019875.7
MercruiserEngineModel 3501991-965.7
MercruiserEngineModel 4201987-897.4
MercruiserEngineModel 4251990-937.4
MercruiserEngineModel 4501995-967.4
MercruiserEngineModel 4651990-948.2
MercruiserEngineModel 5.0L1987-955
MercruiserEngineModel 5.7L1985-965.7
MercruiserEngineModel 5001990-018.9
MercruiserEngineModel 5001994-008.2
MercruiserEngineModel 525SC1991-977.4
MercruiserEngineModel 600SC Gen IV1991-968.2
MercruiserEngineModel 600SC Gen V1991-968.2
MercruiserEngineModel 600SC1997-988.2
MercruiserEngineModel 7.4L1989-977.4
MercruiserEngineModel 8.2L1990-968.2
MercruiserEngineModel 800SC1993-989.4
MercruiserMarine - Inboard & OutboardModel 1201987-892.5
MercruiserMarine - Inboard & OutboardModel 1401983-863
MercruiserMarine - Inboard & OutboardModel 1751987-924.3
MercruiserMarine - Inboard & OutboardModel 1851983-843.8
MercruiserMarine - Inboard & OutboardModel 1851985-874.3
MercruiserMarine - Inboard & OutboardModel 2.5L1987-892.5
MercruiserMarine - Inboard & OutboardModel 2001985-875
MercruiserMarine - Inboard & OutboardModel 2051985-914.3
MercruiserMarine - Inboard & OutboardModel 2281982-845
MercruiserMarine - Inboard & OutboardModel 2301985-875
MercruiserMarine - Inboard & OutboardModel 26019875.7
MercruiserMarine - Inboard & OutboardModel 3.01987-953
MercruiserMarine - Inboard & OutboardModel 3.0LX1987-953
MercruiserMarine - Inboard & OutboardModel 3301982-877.4
MercruiserMarine - Inboard & OutboardModel 3501986-965.7
MercruiserMarine - Inboard & OutboardModel 4.3L1988-964.3
MercruiserMarine - Inboard & OutboardModel 4.3LX1988-964.3
MercruiserMarine - Inboard & OutboardModel 4541986-977.4
MercruiserMarine - Inboard & OutboardModel 5.0LX1988-955
MercruiserMarine - Inboard & OutboardModel 5.7L1988-965.7
MercruiserMarine - Inboard & OutboardModel 5.7LX19965.7
MercruiserMarine - Inboard & OutboardModel 5021990-938.2
MercruiserMarine - Inboard & OutboardModel 7.4L1988-977.4

Replaces These Part Numbers

MANDOA000B0331
MANDOAC155603
MANDOAC155604
MANDOAR150
MANDOAR150AA
MANDOAR150BA
MERCURY MARINE12449
MERCURY MARINE19685
MERCURY MARINE817119
MERCURY MARINE817119-1
MERCURY MARINE817119-2
MERCURY MARINE817119A1
MERCURY MARINE817119A4
REMYRA00123
VALEO600117
VALEOA000B0331

Frequently Asked Questions

Q: Do I need a larger charge wire for a High Output unit?
A: The high amp unit will operate better than stock, but not to its full potential without a larger charge wire. It’s the same reason firetrucks do not use garden hoses. It is IMPARATIVE to have proper charge and ground cables.

Q: Does a High Amp unit cause any damage to my battery or my vehicles charging system?
A: As long as it is installed properly with battery in good condition, then no. A High Output unit works exactly like a factory unit and only produces what is being demanded. No alternator works continuously at full output. Higher amperage is not bad and will not hurt a battery, but high voltage will blow one up.

Q: Will aftermarket underdrive pulleys (crankshaft power pulley) have any effect on my alternator?
A: Yes, underdrive crankshaft pulleys slow all the components (power steering, a/c, and alternator) to provide more power to the rear wheels. In some cases, the charging systems will fall totally on the battery at idle and completely stop charging.

Q: Where is the best place to get a voltage reading of the alternator output?
A: You’ll get the most accurate voltage reading from the back of the alternator at the main charge post that runs directly to the battery. This must be done while the vehicle is running.

Q: Why is the pulley on a high amp alternator smaller than my stock pulley?
A: The smaller pulley advances the power curve of the alternator just slightly, which produces a little more amperage around the idle if needed.

Q: Will I need a smaller belt for my high amp unit?
A: This varies by application because not all belts and belt tensioners are in the same condition. The tensioner will always tell you if you need a new belt or not. If it’s in range, you will not. If it is out, you will. Generally, you will need a belt that is one inch shorter than stock. You should have no problem finding a replacement wherever you buy your parts. V belt applications simply re-adjust your belt tensions to 3/8” deflection.

Q: What is the difference between a one wire, self-exciting and a self-energizing regulator?
A: Nothing. They are all exactly the same. Different manufacturers use different terms for marketing. The only wire to hook up is the charge wire to the battery. This does require modification for the alternator charge light on the dash.

Q: My stock unit used a five-groove pulley, and you sent my high amp alternator with a 6 groove. Why and what can I do?
A: 5 groove overdrive pullies are not produced. Install the belt on the back groove of the pulley closest to the fan or body of the alternator. The fan is internal, and this application will work just fine.

Q: Can your alternator be run in dual or triple alternator applications?
A: Yes. When wired and mounted correctly, the alternator can run in either dual or triple applications.

Q: Will I need a new battery with a high amp alternator?
A: If your battery is in good condition, and in spec of its OEM rating, then no. Your battery should work equally well with either the OEM and a High Amp unit.

Customer Reviews

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