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Tach not working

Jerryjerry05

Jerryjerry05

Outstanding Contributor
98 75hp 3cyl.
Runs ok.
The tach is new.
It's set right for the motor.
It does nothing on any other settings.
It doesn't jump or move when the motors started.
The leads from the motor
Black, grey, purple.
The grey and purple both have voltage. The purple is the power lead and the grey is the tach lead.
The grey is hooked into the rectifier and all 3 lugs on rectifier have voltage.
Hope I gave enough info.
This is on a Mercury

Thanks,Jerry
 
Did you do try and continuity test from the grey lead on the rectifier to the grey lead on the tach to make sure your wire is not damaged? Do you have 12v at the tach for power?
 
Thanks, for the help.
Yes to both questions.
The purple is the power lead and it has 12v.
The continuity is good. No shorts.
It seems to pick up power (12v)from the regulator.
It has 12 volt from the grey lead?????
 
Interesting.. Usually when Tach issues are reported its due to the rectifier/regulator as that is where they get the signal.. They are very inexpensive to replace.. I know on my 115 it was only 20.00 for a new one. Might look into replacing yours?
 
Make sure the ground to the tach is good. It's normally grounded through the mount - clean up the ground lead and make sure it's actually going to ground.
 
Jerry..the grey wire should have 0 volts with engine off and key on, at idle you should have 5 volts on grey and it will increase with rpm, also does tach needle move or fall to 0 when key turned on.

  1. Voltages with engine running should be: IGN to GND Terminal: 12 VDC minimum. SEND to GND: 5 VAC minimum at idle. If you don't get the sender-to-ground voltages shown, voltage rectifier (converts AC to DC voltage) may be weakening/bad. Have it checked.
 
the regulator or rectifier does not put out a flat line dc...flip your multimeter to ac and you should read the ripple..if you read 12 volts dc and nothing on ac you are reading the battery output only...the pulses is what make the tach read...
 
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Mine is more than 3X that.
Gotta find out from the owner if the battery keeps dying.
Ground and connections are good.
Seem like the motor isn't charging either.

I just don't understand why there is 12v coming from the grey lead.
The lead comes from the front of the motor in a cable.
Gonna have to look into it further???
Will look into the pulse in the am.
The key off 12v at the grey lead.


THANKS for the help.
 
i dont have a wiring diagram but i would expect to see 12volts there with the key off....that is your battery output....
 
On the rectifier: the middle post has a grey lead from the engine harness.
It goes to a grey lead up to the dash.
The grey from the engine harness has 12v
The top post has 2 yellow leads and so does the bottom post.
The top and bottom post(yellow leads) have 6v if the key is on or not.
I haven't unhooked the yellow leads to check voltage.

Anyone know how to test a rectifier?
 
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