Tachometer doesn't work, 90 HP Mariner

[Jerry900]

Does a tachometer that works on an Evinrude 50 HP work on a Mariner 90HP?
I bought a used tachometer last year and hooked it up to my Evinrude and it worked just fine. Two months ago I disconnected the tac. Today I hooked it up to my 90HP Mariner and the needle just sits at 0. I checked the voltages at the control box. I have ground and +12v. The voltage increases when the motor is running. The TAC signal is a sign wave going between 0 volts and 5 volts.

Is this the right voltage for the TAC signal? Do I need a different TAC?

 

[Chris1956]

Re: Tachometer doesn't work, 90 HP Mariner

The answer is it depends on what kind of tach you have. Most are universal, and will work with both. Who is the maker of the tach? Does it have a 12P or 6C setting? Those are Merc settings.

 

[Jerry900]

Re: Tachometer doesn't work, 90 HP Mariner

The only marks that might indicate who made the tac are an M with a box around it inside a circle. There is a label that says
"174887 For use on 5, 6 pul/rev., alternator equiped outboards and 6 pul/rev. OMC Sea Driver engines". There is a switch marked PUL/Rev. with positions marked witj 2,3,4,6,5. I think pul/rev. must mean pulses per revolution.

 

[Chris1956]

Re: Tachometer doesn't work, 90 HP Mariner

Sounds decidedly like an OMC product. Try 6P, maybe you will get lucky....

 

[Barnacle_Bill]

Re: Tachometer doesn't work, 90 HP Mariner

Test your rectifier. 5V (AC) is not enough for the tach or for charging the battery..

 

[Jerry900]

Re: Tachometer doesn't work, 90 HP Mariner

Last time I checked the battery was being charged ok. But, I'll check it tomorrow and let you know.

 

[Jerry900]

Re: Tachometer doesn't work, 90 HP Mariner

OK. I checked the battery voltage. With the motor off, I got 12.3 volts. With the motor on and reved up, I got 15.2 volts. From that I think the rectifier and the AC to it are ok. Now I'm thinking I have a bad connection on the gray wire between the rectifier and the plug on the control box. I'll keep checking and let you know.

 

[Jerry900]

Re: Tachometer doesn't work, 90 HP Mariner

My TAC is now working. I had to move the gray TAC signal wire from one yellow wire on the rectifier to the other. Apparently the motor can output the TAC signal at two different voltage levels. The original yellow wire has 1.3 rms volts to ground and the other has 8.0 rms volts to ground. My TAC works at 8.0 volts but not at 1.3 volts. This has been an education for me!

 

[Barnacle_Bill]

Re: Tachometer doesn't work, 90 HP Mariner

Your tach should work off either yellow wire coming from the stator. I would still test the rectifier.