Testing a voltmeter gauge

[Robob]

I replaced the rectifier on my Evinrude because of erratic tachometer movement and a battery reading of only 11.9 volts. It now shows about 12.65 volts on a digital multimeter so I'm confident the battery is being charged.

The volt meter in the instrument panel moves a little but only shows 11 volts at idle or 3500-4000 RPM on a now steady tach.

How do I hook up the multimeter to see how much voltage is really getting to it?

Replacing it is not hard but I would like to know it's needed.

Thanks,

Bob on Tampa Bay

[GoneFission]

Check the voltage on the back of the panel meter.  If the reading on the panel meter does not match your volt meter, something ain't right...   If you get 11 volts on the back of the panel meter, you probably have a loose or corroded connection somewhere.  

Hope this helps - good luck!

[seabob4]

John's right.  The voltmeter at the helm should mimic the readings on your batt...

[John Jones]

I gave up on finding a marine voltmeter that would read even close.  I just learned how far off it is and go with that.  My current voltmeter reads a heavy 12V when my Fluke 87 reads 13.5.  If it's touching 12 I know I'm okay.

[labboss2003]

Did the rectifier fix the tach prob?

[Robob]

It looks like the rectifier fixed the tach problem, it now seems to read correctly.

I need to know if the gray or purple wire on the back of the volt meter is positive and the black wire negative. It may have been rewired and the colors messed up so I'll have to experiment with the probes on the multimeter.

Thanks in advance,


Bob on Tampa Bay

[GoneFission]

It looks like the rectifier fixed the tach problem, it now seems to read correctly.

I need to know if the gray or purple wire on the back of the volt meter is positive and the black wire negative. It may have been rewired and the colors messed up so I'll have to experiment with the probes on the multimeter.

You've got the wires right, and if you had them wrong, it would not give any reading - it would peg on zero.

[Robob]

Thank you:-)

Bob on Tampa Bay

[seabob4]

Bob,
Just so you know, on OMC motors the purple wire is 12V+ from the motor, powers up your tach, trim, volt, and fuel gauges.

[RebelYell]

Bob,
Just so you know, on OMC motors the purple wire is 12V+ from the motor, powers up your tach, trim, volt, and fuel gauges.

Same thing on my Mariner. Power and ground are daisy chained from meter to meter along the back of my instrument panel. I rewired the whole boat ( 12 V ) last year...

 :|

[Robob]

Now I was able to test the voltmeter and got 11.9 volts (which is what the meter is reading) with my new digital multimeter while the motor idled on the earmuffs.

Testing the battery terminals showed 12.65 volts so I'm not concerned about it being charged.

Joints are clean and the wires are tight on termninals on the back of the voltmeter.

I guess I'll have to chase down the wires to see if there's a bad connection somewhere.

Any other ideas?

Thanks for all your help,

Bob on Tampa Bay

[John Jones]

If you have 11.9 at the meter and 12.65 at the battery you are pretty much assured it's a bad connection or a bad wire (when you strip a wire and the copper is brown or black  and flaky you can count on it not being able to handle the load).  Remember that the voltmeter is practically a zero load too.  When my motor main battery cables went bad I could read battery voltage at the motor with the switch off.  Turn the switch on and it dropped some.  Try to crank and it dropped to 2.6 volts at the motor all due to those brown flaky wires.

[seabob4]

On badly corroded breakers, I have seen voltage drops of almost 3V from the input to the output sides...

[John Jones]

I have never had a breaker on a boat that did not give trouble sooner or later, especially exposed breakers.  

Waterproof    :(

[seabob4]

JJ,
The little rubber caps may help...on the reset button, not the back side! :x