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New Alternator or replace the voltage regulator

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  • New Alternator or replace the voltage regulator

    I have a 1989 Baja with the Merc 5.7 sterndrive. I tried searching, and found lots of issues regarding alternators, but none that answered my question.

    Background:
    I have been experiencing some electrical issues. While out on the water, I noticed that my voltage gauge would jump to around 15-16 while on plane and then jump back to normal. The very next time I go to take the boat out, I get a few spins on the starter and then the battery is too weak to start it. So, I check all the wiring to be sure everything is tight and corrosion free. After this, I also had the battery tested since I knew it was about 5 years old. It turned out that it was bad. So I replaced it. After installation, I took the boat out the following weekend. Everything seemed fine, but I would still get the occasional quick jump to the 15-16 volts on the gauge. This last time I took it out, while on plane, the gauge pegged to the high side and I could hear what sounded like a squeal (only while the gauge was pegged). While headed to the dock for lunch the gauge dropped to 12 volts. When I returned to the boat and started it, the gauge was still showing 12 volts regardless of RPM.


    Equipment: The alternator appears to be the original alternator to the boat. The date code shows 08-88. It is a Mando. I had it tested and it appeared to be working correctly when tested. The guy who tested it runs a battery/alternator/repair shop local to me. He indicated that the high voltage reading would likely be caused by the voltage regulator.


    Question: Should I replace the whole alternator or just the voltage regulator?


    Thank you in advanced.
    1989 Baja SunSport 196
    5.7 Mercruiser, Alpha 1

    Sparta, Mi

  • #2
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    Agree the high voltage would be from the regulator, but with the squeal I would just replace it. The bearings would need replacing, and while your local guy should be able to do it, if it was mine I would get another one.
    94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
    95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
    07 SeaDoo GTX
    Raw Water Pump Maintenance
    Merc Adults Only

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