Tach help on Mercury 115

[detchon]

I have a 1993 Mercury 115 and I have been having problems with the tach and the charging system (read my other posts!!).
I narrowed my previous problem down to a voltage regulator, which I replaced. After doing that, the charging system worked and the tach worked fine for about 20min. I shut off the motor and restarted and now the tach doesn't work anymore. The needle moves up and down at random going a various speeds. The boat is still charging the battery.
I did the bench test on the new voltage regulator after this happened, and everything checks out but the grey tach wire. I am not getting any readings on it.
Is it possible that the tach part of the voltage regulator would fail while leaving the other parts to work properly and what would cause it to fail in the first place?
Any help would be appreciated as I am becoming increasingly frustrated with this problem.
Thanks.

 

[canoemang]

Re: Tach help on Mercury 115

My tach was doing tht and it was my rectifier..

 

[bunker108]

Re: Tach help on Mercury 115

I am having problems with my tach as well...granted it's a 72 115, but I have concluded that my rectifier is bad as well.

 

[Chris1956]

Re: Tach help on Mercury 115

On the OP's motor, the rectifier is built into the voltage regulator. I do not know if the grey wire can give a bad signal for the tach and the VR still function correctly, however, you may hook the tach signal wire to one of the yellow stator wires. That will give the correct tach signal.

 

[Chris1956]

Re: Tach help on Mercury 115

Do you have any AC voltage going to the battery?

 

[detchon]

Re: Tach help on Mercury 115

Yes, the battery is charging when the engine is running, that is how I know that the new VR is working. I just can't figure out why the tach would stop working when the VR is working. So you suggest that I try and hook the grey tach wire to one of the yellow stator wires coming out the VR?

 

[Chris1956]

Re: Tach help on Mercury 115

Yes, hook the grey tach wire to one of the yellow stator wires and see if the tach functions properly.

I asked if you had any alternating current (AC) present at the battery? if you do, it is likely the VR has a bad diode.

 

[Bill kubiak]

Re: Tach help on Mercury 115

I had a similar problem with my Mercruiser inboard, it turned out the tach was bad

 

[detchon]

Re: Tach help on Mercury 115

I attached the grey tach wire right onto my terminal block where the yellow wire from the stator joins the yellow wire going to the VR and my tach still isn't working properly. Even when the key is off, the needle never falls below the 1000 RPM range and at WOT it goes into the 7000 RPM range which I know is not correct. Should I be getting an accurate tach by this method and if I'm not, does that mean that there is something wrong with my tach?
Also, my trim gauge doesn't work at all and I checked the resistence at the trim sender and it appears to be working properly. Could the tach and trim gauge be connected in failing to work?
I checked the voltage at both gauges with the key on and I am only getting 4.5v on each gauge. Should I not be getting 12v?

Any help would be appreciated.