Re: Volvo 12v alternator

Mike Ondra

So here’s a couple of things that we learned about the alternator systems on the Volvo. Our original problem was that the 24 V alternator was not charging until fairly high rpm above 1800. Ultimately what we determine was that the warning light on the 24 v panel in the main salon was burned out therefore not completing the exciter circuit. When replaced by a new indicator light the 24 V system behaved properly.

During troubleshooting we noticed the yellow wire on the 12 V alternator was disconnected. It must’ve happened recently because the 12 V alternator was not putting out any voltage today but we didn’t have a problem with the battery in the past several weeks.. The battery was down to 12.4 V. Interestingly the tachometer did not work either, Which makes sense since it’s connected with the black and gray wire to the alternator picking up the unrectified voltage to pace the RPM. 

Turns out that the yellow wire should have been and perhaps was attached to a tab on the main positive lug on the alternator to the battery. That yellow wire appears to feed the 12 V voltage regulator.

Anyway, with the 24 V warning light replaced and the yellow wire connected to the positive lug on the 12 V alternator everything is working great. Thank you all for your input. Note that the above is our rationalization for what happened and may not necessarily be 100% correct.

Aletes SM240

On Oct 27, 2020, at 1:56 PM, CW Bill Rouse <brouse@...> wrote:


I am not sure if the following applies to the Volvo 12v alternator, but it applies to the Yanmar 12v alternator:

There is an unused tachometer output wire on all SM Yanmar 12v alternators. See the photo below. Please let me know if yours is the tachometer wire.

Also, possibly there is an issue with the "excite circuit." The alternator will self-excite at higher rpm. Try revving the engine in neutral to 1800 rpm.

CW Bill Rouse Amel Owners Yacht School
Address: 720 Winnie, Galveston Island, Texas 77550 
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On Tue, Oct 27, 2020 at 10:28 AM Mike Ondra via <> wrote:
Lost output from 12 V alternator. Doing initial  trouble shooting  trying to understand the function of the short yellow wire which arises from near the voltage regulator and is not connected to anything else at the female terminal end. Should it be? And to what?

Mike Ondra
Aletes SM 240

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