Mercury 115 Tachometer Problem

[BrockSolid]

Tach started last summer with erratic readings.
Started boat up yesterday and seemed to be working fine. Then started drifting and dropping. Would jump around when tapping on screen. Not working at all today.
Checked voltage at the tach and getting 12.36 volts at idle.
Any suggestions appreciated.

 

[QBhoy]

Is this a 2 stroke or modern 4 stroke we’re talking ? 12.anything bolts ain’t too great when running on either, but absolutely not normal on the latter. What voltage are you getting to the battery at idle ? If that’s healthier, back to the dash and assume poor connectivity

 

[BrockSolid]

It’s a 1996 2 stroke.

 

[Chris1956]

Check the voltage, ground and stator signal at the tach. Obviously the battery voltage is DC. Expect the stator signal to be AC.

If the voltage jumps around, you likely have wiring issues. if the voltages are steady, the tach could be bad. They do not last forever.

 

[BrockSolid]

Just checked voltages on battery and tach.
12.4 at battery. 12.36 at tach.
I think I have a regulator or stator issue.
Not running battery shows 12.4 volts.
Engine running… volts drop to 12.35.
Bites tests are at top of battery posts.

 

[BrockSolid]

Just checked voltages on battery and tach.
12.4 at battery. 12.36 at tach.
I think I have a regulator or stator issue.
Not running battery shows 12.4 volts.
Engine running… volts drop to 12.35.
Bites tests are at top of battery posts.

Both tests at top of battery posts

 

[Chris1956]

The voltage drop when running is a bad sign. Did you check for AC voltage at the tach? If you get some, the stator is likely good.

Depending on the year of the motor, it will have a rectifier, voltage regulator or perhaps both. Those are more likely to fail (and cheaper) that the stator.

The internet will tell you how to test the rectifier using an ohmmeter. Voltage regulators are harder to test, so if the stator is good, the wiring is good and she won't charge, the voltage regulator is likely bad. Sierra likely makes an aftermarket replacement.

 

[BrockSolid]

Pulled cowl off.
Red and yellow look burned. Small crack in VR (identified by screwdriver).
Thoughts?

 

[BrockSolid]

Pics at VR

 

[Chris1956]

Not sure that is definitive. A voltage test would help determine if the VR is good.

 

[BrockSolid]

Not sure that is definitive. A voltage test would help determine if the VR is good.

I’ve read so much in this already, with many differing and confusing suggestions on testing.
How would I volt test it? As mentioned, I’ve tested on the battery posts while running and non running.

 

[guitarplaya39]

Following. Same tach issues and identical burned-looking VR wires on my '93 75hp 2 stroke.

 

[Chris1956]

You need to test the yellow wires for AC voltage when the engine is running. So either stick the voltmeter leads into the yellow bullet connectors, and start the engine, or disconnect the yellow wires and test them with the engine running. If you find AC voltage on the yellow wires, the stator is good. Next test is for AC voltage on the grey wire. If you find that, the tach is likely bad. If no AC voltage on the grey wire, the VR is likely bad.


if you disconnect the red wires, and start the engine, the VR will immediately blow, if it is good.

 

[BrockSolid]

You need to test the yellow wires for AC voltage when the engine is running. So either stick the voltmeter leads into the yellow bullet connectors, and start the engine, or disconnect the yellow wires and test them with the engine running. If you find AC voltage on the yellow wires, the stator is good. Next test is for AC voltage on the grey wire. If you find that, the tach is likely bad. If no AC voltage on the grey wire, the VR is likely bad.


if you disconnect the red wires, and start the engine, the VR will immediately blow, if it is good.

Thanks for the info. When testing the gray wire, would I just post my black multimeter lead onto a ground somewhere?

 

[Chris1956]

Yes, the grey wire is the same as either of the yellow wires. They just pull it thru for convenience.

I would not think that the regulator could be good, and the grey wire not putting out the tach signal, however, if that happens, you can substitute either of the yellow wires to get a signal to the tach.

 

[BrockSolid]

Turns out it was the rectifier/VR.
Put the new one in and tach fired right up.
Voltage at the battery while running is now 14.3.
Hopefully this resolves some recent issues.
Also found a completely corroded positive battery wire from engine to battery.
Replaced with 4 gauge starter wire and soldered copper leads. Instant start up now.
Appreciate all the help.

 

[guitarplaya39]

Turns out it was the rectifier/VR.
Put the new one in and tach fired right up.
Voltage at the battery while running is now 14.3.
Hopefully this resolves some recent issues.
Also found a completely corroded positive battery wire from engine to battery.
Replaced with 4 gauge starter wire and soldered copper leads. Instant start up now.
Appreciate all the help.

Did you check for AC voltage on the grey wire before switching it out? If so, what did you get?