How to Remove Alternator Mercury Optimax 90hp


What are the correct procedures for taking off the generator on a 2005 Mercury Optimax 90 horsepower engine? My boat motor alternator does not seem to be converting sufficient electrical energy to charge the battery.

My battery is good but it died and I suspect the alternator is not generating enough electricity.

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Christian 3 years 2020-12-10T05:17:40+00:00 3 Answers 1063 views Beginner 1

Answers ( 3 )


    How to Remove Alternator

    1. Take off the OptiMax engine top cowling.

    2. Detach the positive and negative battery cables.

    3. Disconnect the wire harness connection from alternator.

    4. Use a serpentine belt tool or breaker bar to loosen the belt tensioner.

    5. Pull out the alternator belt.

    6. Remove the two bolts that hold down the alternator.

    a. Attaching Bolts. b. Harnesses (hidden). c. Belt Tensioner.

    Reverse the procedures to reinstall the alternator but be certain the belt is inserted back into the groves of the compressor fully, alternator and flywheel.

    Best answer

      How can I test the alternator without removing it from the engine? It looks pretty simple to take off but I don’t live near a marine or automotive part store that can test my alternator and I don’t want to replace it if it’s not necessary. How do I test it myself?


        Testing alternator without removing it.

        I am not a mechanic but it is said you can just use this to test the alternator. It is a cheaper alternative but not 100 percent accurate. Follow the installation instructions that come with it.

        Although the factory service manual says you need an ammeter that is capable of reading 60+ amperes to perform output load test. Be certain the battery is fully charged before the test and that no accessories on the boat are on while performing the output load test.

        1. Turn off boat engine.

        2. Install ammeter in series between positive + of battery and terminal B on alternator. If you’re using a clamp on style ammeter then position the clamp over alternator output lead.

        3. Start the Mercury Optimax and allow it to warm up. Then advance the RPM to 2000.

        4. Trim the Mercury Optimax engine to the full down position and while loading trim pump in the full down position, watch the reading on the ammeter. The alternator output should be a minimum of 45 amperes while the voltage at the battery should be anywhere between 12.5 to 14.5 volts. If it does not reach the correct output, remove and replace the alternator with a new one.

        Remember that if the battery is defective or not fully charged then the voltage will be below 12.5 volts and the amperage will be correspondingly lower.

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