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Thread: V6 Mercury tachometer
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08-02-2020, 08:18 PM #1Team Member
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V6 Mercury tachometer
Having trouble with a V6 Mariner Mag3 factory tack which is unreliable, will work ok occasionally but the will bounce around and then return to zero. This can occur at any rpm and I have tried two different tacks, same results. Have rewired a new group d wire directly from the battery to the gauge. Same results. Then ran a totally new sender wire from the regulator to the gauge with the same results. Replaced the 12 volt accessory wire to the gauge and again the same results.
How do I test the regulator output (grey wire coming out of the regular) should I be reading a low DC voltage at idle and increasing voltage with RPM or is there a different test I could perform. Have eliminated all other possible problems I can think of.
Appreciate any advise as there is no tack troubleshooting info in my manual.
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08-02-2020, 08:45 PM #2
Could be a rectifier. They make tach do strange things. If your Volts are running lower than normal also, it is probably the rectifier
"The Flying Clamato"
...This ain't no Party, This ain't no Disco, this ain't no foolin around..."Talking Heads - Life During Wartime"
The G-Train has left the station.
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08-02-2020, 09:16 PM #3Team Member
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Battery voltage remains good and starting has never been a problem with lots of cranking power, volt gauge indicates correct voltage with discharge and positive charge rate deflections once thru starting and trim operation.
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08-03-2020, 03:09 AM #4
You can connect a multimeter to the grey rectifier wire
set it to herz
If it is not stable the rectifier is probably suspect
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08-03-2020, 11:49 AM #5
If you have regulators with grey wire the rectifier is built into the regulator. Try switching grey wire to other regulator if you have 2.
Dave1980 Cougar 19 tunnel,90 2.4L Bridgeport EFI in middle of restoration.
1988 BAJA Sunsport 186, 96 225 Pro Max
79 12' Auminum, 95 Merc 9.9
RIP Stu
"So many idiots, so few bullets"
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08-03-2020, 02:53 PM #65000 RPM
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Normal Tach Rectifier output is shown on the right hand side of drawing below "Half wave" which drives the tachometer "upscale" only .
The wave form on the left is what occurs with failed (or failing diodes ) and drives the tach needle up and down causing it to be unstable . Using a digital multimeter with hertz function you should read 6 positive pulses per engine revolution .
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08-03-2020, 05:28 PM #7Team Member
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Yes this engine has 2 rectifier's. I will give that a try next time I am out to the lake. Thanx and hopefully that will solve the problem.
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08-03-2020, 05:31 PM #8Team Member
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A big thanx to all whom have suggested easy troubleshooting tips. Will be a few days before I get back to the boat to try but will keep you's posted.
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08-04-2020, 01:39 AM #9
As pointed out above, it is most likely the rectifier.
If the tach works like it should when connected to the other half of the rectifier, you know for sure.
Mercury rectifiers are junk. There is an aftermarket part for an Opel that gets the job done and lives much longer at a fraction of the price.__PRESENTMarkus' Performance Boating Links:
www.toastedmarshmallow.com/performance
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08-05-2020, 05:41 PM #105000 RPM
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fought this same thing a couple years ago. bad rectifier.
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