Re: 2001 mercury 90 hp voltage question
I have the exact engine only a couple thousand numbers higher. My manual goes back to '94 and all these engines were a lot alike so this probably is accurate for yours.
The voltage regulator has 2 yellow wires from the stator for inputs and gnd and two red wires for regulated voltage output and a gray wire for pulses to run the tach. Since the whole thing crapped out I think I would look for a problem towards the stator.
Per the manual: Separate the yellow leads going from the stator into the regulator. With an ohm meter on the lowest scale measure the resistance of the stator via the leads. It should be between 0.16 to 0.19 ohms (ambient temp 65-85 F) If outside that range, colder will be more and hotter less....copper molecules are more active as they get hotter so effort to move them is less. Then check one lead to ground and it should be an open circuit. If either of these tests fail, expect your regulator module to be functioning and the problem is the stator. That's bad news. I'd much rather have it the other way personally, but we don't get to select our malfunctions.
I believe you have an open wire in/to the stator because of what you said, but maybe not...see later. The rectifier module is a full wave bridge rectifier consisting of 4 diodes in a bridge configuration....2 for each half cycle of the ac input. It rectifies sine waves into half sine wave dc voltage...takes the half wave on the bottom of zero and puts it on the top making two + polarity half cycle waves. Additionally it has a series regulator that controls voltage and current to help to limit the current to 16 amps max on a discharged battery and 14.5v max on a charged battery. I don't know where the tach output comes off; before or after the regulator and that could be important to know in troubleshooting.
If the tach comes off after the regulator, it could be the regulator circuit has open circuited which would point to the regulator module. If your stator tests pass then this would probably be your smoking gun. But to absolutely know for sure without substitution, you would have to test the stator output under load for proper voltage and current. That gets a little complicated for the layman....you need a suitable load and metering. These half waves are fed to the tach and it counts them. They are also fed to the battery as "pulses" to pump energy into the battery.
HTH,
Mark
