1999 Merc 125 Carb. No tach, no volt gauge.

[mudweiser]

Helping a new neighbor with his boat. 1999 Bayliner 17ft. The tach is stuck at 800 rpm's. and the volt gauge dont work either. I was only able to test the gauges with the key on, but he said the tach dont work. The boat also has a bog from holeshot going to wideopen. But thats another issue i know. Anyways, i put a test light to all the wires on the volt. With a meter when the key is on in run position but w/o the motor running we got like 11.89 volts. It has power to the light for the gauge, it has a good ground through the lights ground wire and it has good voltage through the gauges positive wire. Then the Tach dont work also. The Tach has good ground good power from the battery. I need to know how to properly test both the volt gauge and the Tach. Thinking this might be a bad rectifier. We have yet tried to apply a good source of 12 volts to the volt gauge. Any insight?

 

[CharlieB]

Re: 1999 Merc 125 Carb. No tach, no volt gauge.

the tach trigger is pulsed by the charging coils of the stator thru the rectifier. Generally, a dead tach is caused by a bad rectifier. Disconnect the rectifier and do an Ohms test, each of the yellow input leads to the red output, then reverse your leads and retest. You should have continuity in one direction and none when you reverse the leads.

Check charging at the battery, read voltage engine off, then start the motor and advance to fast idle and watch the voltage rise. No rise, no charging.

 

[mudweiser]

Re: 1999 Merc 125 Carb. No tach, no volt gauge.

Okay, i was off by 1 year. It's a 2000 motor. Anyways, i tested the rectifier. Motor off testing at battery 12.20 volts. Motor running at battery on hi idle 12.83 volts. I was able to get cont both ways testing the rectifier the way you mentiones. If i test one way it was steady ohms. When i reversed the leads the meter kept dropping. I'm not the best with a meter. This was a craftsman multi range set to ohms.
I spoke with a local speed shop. They said to test the yellow wires from the stator. So we fired the motor, set the meter on ac current at hi idle. It only showed .9XX on AC current auto range meter. Do you have any insight here? I did apply a good battery test box to the volt gauge and it did not registure, so i kow the gauge is bad. Not sure about the tach.

 

[mudweiser]

Re: 1999 Merc 125 Carb. No tach, no volt gauge.

Can anyone tell me if a 2002 Mercury 125hp stator will fit on a 1999 125hp motor? They look the same, they have the same amount and color of wires.