# Yanmar 2GM20F Tachometer troubleshooting



## ChuckA (Dec 28, 2008)

My tach stopped working. The engine is running fine. Reading the service manual, I checked for voltage at the red/black leads to the tach and found none (should have ~12 V with key on). I traced the red wire back to the switch on the instrument panel. There is no voltage at the switch terminal (# 15 on the drawing) which is supposed to supply voltage to the tach. I'm looking for a schematic for the switch on instrument panel or suggestions on where to look for an open circuit.


yanmar instrument panel_1 by chuckanastasia, on Flickr


yanmar instrument panel_expl_1 by chuckanastasia, on Flickr


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## Skipper Jer (Aug 26, 2008)

I did find a service manual in pdf format on the web. Hold one,.........ahh,
j30.us/files/yanmar-manual.pdf
Take a look towards the end of the manual, there is a diagram showing the tach wiring.


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## rikhall (Feb 7, 2008)

All of the times that my Yanmar tach quit working it was because some idiot (usually me) had bumped the wires on the engine and one had come loose.

Start simple and go from there.

Rik


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## mm2187 (Sep 8, 2011)

If that panel is the same as my engine the toggle switch you are talking about only allows you to illuminate the tach and to allow you to test the alarm. It has nothing to do with powering the tachometer.


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## imagine2frolic (Aug 7, 2008)

I have the same panel with a 3GM30F, and my problem has been a loose wire on the sender at the back of the block........*i2f*


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## ChuckA (Dec 28, 2008)

Thanks Captainmeme, that's a helpful manual. Here is the schematic from p 56. *Now I see where I went wrong.* This is from the trouble shooting guide I was looking at from a Yanmar workshop manual.



> Tachometer Gauge
> To check the tachometer gauge unit, proceed as follows:
> 1. Disconnect the red/black and black wire leads from the
> tachometer. With the key switch ON, measure the voltage
> ...


I confused the red/black for the bulb with the red and black leads. I'll check it again in the morning.


wiring diagram_1 by chuckanastasia, on Flickr

I appreciate the help!


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## MooGroc (Sep 22, 2009)

I have a similar problem with my Yanmar 3JH3E. Can anyone tell me where the rpm sensor is on the engine? Is it flywheel driven?

Lawrence


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## RichH (Jul 10, 2000)

Carefully look for corrosion on the tach sending unit at the bellhousing/flywheel and all the connectors on this entire circuit. Yanmar still uses non-tinned wire on its control panels and the tack sending unit (and the starter solenoid) wire connectors are quite vulnerable. Physically look at the connector as a multimeter reading when the connector is still 'wetted' by the atmospheric moisture will provide (some) continuity ... let it dry out by engine heating and the corrosion will show as an 'open'.


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## ChuckA (Dec 28, 2008)

Lawrence: The tach sender is on the flywheel housing near the transmission.


Yanmar 2GM20F tach sender by chuckanastasia, on Flickr


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## MooGroc (Sep 22, 2009)

Thanks RichH and ChuckA - especially for the picture. I'll start limbering
up for the contortions I'll have to go into to get at it this weekend.

Lawrence


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## ChuckA (Dec 28, 2008)

I finished my troubleshooting yesterday and it looks like the outcome is to replace the tach gauge. 

I have battery voltage at the tachometer terminals and can read an AC signal of a couple of volts at the gauge connector from the sender. 

After confirming the voltage, I took out the instrument panel tapped on and shook the gauge, but no luck on re-assembly. I'll shop around a bit for the replacement. I saw some prices online about $150.

FYI, here are the trouble shooting guidelines for the sender:

Tachometer Sender
To check the tachometer sender, proceed as follows:
1. Disconnect the leads from the sender (Figure 29).
2. With the engine slopped, use an ohmmeter to check the
resistance between the sender terminals. Resistance
should be 1500-1700 ohms.
3. Run the engine. Measure the alternating current voltage
between the sender terminals. The voltage reading
should be at least one volt.
4. If the sender fails either test, replace the sender.


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