No tach,no charging

Chris1956 · 2026-09-11T09:03:39-0600

You can also, disconnect the yellow wires and run the motor on a flusher and look for AC voltage on the two yellow wires. I would expect 100VAC or less, so start with the meter set to a high AC scale.

Dukedog · 2026-09-11T12:23:44-0600

tha one in your picture is a combination reg/rectifier.. is same as as most mercs of tha early ninties up to somewhere in tha 2000's.. ready available on most parts sites.... try ta stay away for tha "real cheap" knock offs....

boscoe99 · 2026-09-11T12:50:34-0600

By serial number your model uses a voltage regulator. Which of course has a rectifier inside.

Single phase AC output from the applicable coil of the stator to the regulator. On the two yellow wires.

DC output from the regulator on the two red wires. Case is grounded.

If the regulator fails to provide the appropriate DC output then check the stator coil output for AC voltage.

Ifishmuskie2 · 2026-09-11T13:04:06-0600

I checked stator output on the two yellow wires and got 12.3 volts. (That’s the battery voltage)
That’s with everything hooked up and running on muffs.
I guess the next step is to replace the stator.
Or can i check it when it’s off the engine?

99yam40 · 2026-09-11T13:19:06-0600

when reading the yellow wires did you have the meter set to AC since that is what is suppose to be on the yellow wires?

Ifishmuskie2 · 2026-09-11T13:27:01-0600

No I had it set to dc volts.

Ifishmuskie2 · 2026-09-11T13:46:26-0600

I just tested the two yellow wires on AC and got zero.

99yam40 · 2026-09-11T14:45:29-0600

was the motor running?
maybe disconnect the yellow wires from the RR and try it again to see if you get anything from that coil

Ifishmuskie2 · 2026-09-11T15:00:21-0600

The engine runs great.
Just no tach and no battery charge.

I found my gear puller I just need a 15/16 socket and I guess I’ll pull the flywheel tomorrow.

Ifishmuskie2 · 2026-09-11T16:06:30-0600

Yes the engine was running when I checked the yellow wires.

boscoe99 · 2026-09-11T18:08:55-0600

Ifishmuskie2 said:
Yes the engine was running when I checked the yellow wires.

If the motor was running at a fast idle and the two yellow wires were unloaded (not connected to the regulator) then the stator is kaput.

No input to the regulator equates to no output from the regulator.

Chris1956 · 2026-09-12T02:32:11-0600

I do not think you should have gotten any DC voltage on the yellow wires. The rectifier in the VR would have prevented that. You might check your voltmeter dc scale on a known DC source, like the battery.

Mc Tool · 2026-09-12T02:59:18-0600

Chris1956 said:
I do not think you should have gotten any DC voltage on the yellow wires. The rectifier in the VR would have prevented that. You might check your voltmeter dc scale on a known DC source, like the battery.

Yellow wires from the alt are before the reg/rect , but if one had the meter set to dc while testing an ac output the meter would show a reading and depending on the dampening function on a particular meter you may see a reasonably stable reading ....however wrong it was .
My Fluke 179 had a reading dampener that can be disabled .

Chris1956 · 2026-09-12T07:27:34-0600

yes, but OP said no AC voltage on the yellow wires, when the engine was running, but DC voltage there? That is not the way it should work.

If there really was DC voltage on the yellow wires, the stator would be an electromagnet and discharge the battery.

Texasmark · 2026-09-12T07:30:27-0600

Ifishmuskie2 said:
I already installed a new one and it didn’t change anything.
I just ran the engine on muffs and the voltage on the yellow wires was12.3. So just the battery voltage.
Now what? Replace the stator?

The AC voltage on the yellow wires is RMS.....Root-Means-Square. It is about 70% of the Rectified and filtered DC peak. 12.3V/.707 = 17.4. Pass it through some diodes and load it down due to resistance in the charging circuit and you wind up with 14.5V which is the tops for most circuits of this sort. My opinion....what you measure is good. Look for any problems elsewhere.

Ifishmuskie2 · 2026-09-12T08:15:25-0600

It went from working great to no charge and no tach.
That’s why I changed the rectifier.
Maybe the new rectifier is ng also.
How do I check it?
I’m going to check everything i can see.

Chris1956 · 2026-09-12T08:24:35-0600

There is no bench test for a voltage regulator that I know of. You could feed it 16VAC and see what it puts out. It should try to put out about 14VDC

Let's see, your furnace thermostat runs on 16VAC, so cannibalize your heating system and go from there.

Ifishmuskie2 · 2026-09-12T08:27:05-0600

When I turn the key the tach moves to zero and the volt gauge moves the 12.5volts

Chris1956 · 2026-09-12T08:28:45-0600

That is normal behavior for the tach.

99yam40 · 2026-09-12T08:33:01-0600

like Boscoe99 said

the yellow wires need to be disconnected from the RR when testing for AC to see if it is putting any AC voltage

No tach,no charging

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