New Alternator or replace the voltage regulator

silverknight

Cadet
Joined
Jul 8, 2011
Messages
9
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.
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
40,582
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.
 
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