Cant Get My Tach To Work

mav6759

Chief Petty Officer
Joined
Jun 25, 2007
Messages
489
I was wondering if someone could give me a had with my tach gauge..I have tried about 6 Different gauges with the same result. I just can get the stupid thing to work...I have to be missing something...When I turn the key the gauge jumps up a little...When I start the motor nothing.. Because I see the gauge move, that tells me I am receiving a signal from somewhere, but the dog on thing just won't work..I even pulled a gauge from a friends boat that we knew worked nothing,,,I played with the pole switch on the back nothing, I traced the purple wire back to the motor it its connected. I believe I have a ground, because the gauge light works...I know i'm receiving some sort of signal because the gauge does more with the switch.....What am I missing...
 

GA_Boater

Honorary Moderator Emeritus
Joined
May 24, 2011
Messages
49,038
It might help if we knew what the h**l motor all these busted tachs are connected to.
 

sam am I

Commander
Joined
Jun 26, 2013
Messages
2,169
...When I turn the key the gauge jumps up a little...
The circuity internal to the tach, when initially being powered inherently can and will cause the tach's needle to jump some, and course, can vary between tach's and manu's


When I start the motor nothing
Since you've checked power and ground(and the needle jumps, usually just mean powers' good and just switched on!), tells you no signal present at tach.


Because I see the gauge move, that tells me I am receiving a signal from somewhere
No!! See above...


What am I missing...
The signal....
 
Last edited:

Alumarine

Captain
Joined
Feb 22, 2005
Messages
3,738
Is it a 4 stroke or 2 stroke motor?
Are you trying 4 stroke or 2 stroke tachs?
 

mav6759

Chief Petty Officer
Joined
Jun 25, 2007
Messages
489
The motor is a 2 stroke, I'm using a 2 stroke tech...so I'm missing the signal from the gray wire. From what I understand the signal is produced by the rectifier...so I'm guessing I may have a bad rectifier....
 

The Force power

Commander
Joined
Feb 3, 2019
Messages
2,350
The motor is a 2 stroke, I'm using a 2 stroke tech...so I'm missing the signal from the gray wire. From what I understand the signal is produced by the rectifier...so I'm guessing I may have a bad rectifier....

The signal IS produced by the Stator! however a faulty Rectifier can cause issues.
Does the Rectifier produce voltage with engine running & how much??
Disconnect/bypass the Rectifier & see if the Tach. starts working
 

sam am I

Commander
Joined
Jun 26, 2013
Messages
2,169
so I'm missing the signal from the gray wire.

I believe (I haven't looked it up...I'm being lazy) 2005 90hp Mercury runs a solid state rec/reg module, so yes, most likely a bad tach output on the the rec/reg (common) or a break in the gray wire somewhere between the rec/reg and the tach (sometimes happens)

From what I understand the signal is produced by the rectifier...

True, well sorta......."Conditioned" by the rec/reg is more like it, as force says above, its originates from the stator's AC pulses.

so I'm guessing I may have a bad rectifier....

Yes but only the tach output (gray wire) is bad sometimes, the rec/reg can still be working enough to charge your batt (should be somewhere around 14V when up at 1500RPM with full'ish charge)
 
Last edited:
Top