115 hp inline 4 mariner 1992 approx tach problems

[paulzz]

hello. i have a 115 hp inline 4 mariner 1992 approx. I replaced the switch box and rectifier last year because the boat would not run on low idle. The tach was intermittent before that. The tach is my problem. I just replaced the tach and it still does not work. What can i do to check the circuits. I think i would now need to replace the Voltage rectifier. I have a shop manual for the motor and i do have the wiring diagram. But it looks like the grey wire coming from the rectifier goes to the wiring harness to the front of the boat for the tach. Any help would be appreciated. Thank you

 

[Texasmark]

Grey wire was the tach wire on my last engine. It uses the rectified voltage from the voltage regulator to count pulses and produce an rpm indication. I don't know the circuit, but what you have is the tach, 12v, ground, the grey wire signal input and the rectifier-regulator as the sending unit.....seems you are on the right track.

 

[444]

Is your battery charging properly when the engine is running? I ask only because if your charging stator is pooched your tach won't work even if you have a brand new tach and rectifier. Ignition is run off a separate stator so it can still run just fine...

 

[paulzz]

Hi, So i put the motor in my water barrel this morning. Ran it and check the voltage on the battery before starting it and than again after. Around 12.5 volts when shut down. When the boat is running the volts are all over the map. From 3 volts all the way to 16 volts. So would this be the stator or the voltage regulator/rectifier? Thank you

 

[Texasmark]

The regulator is shot. 16v at higher rpms is unregulated. Starting at around 1000 rpms (service manual talking here) the red stator will deliver 16 amperes at a max of 14.5v...rising as rpms rise.