1985 Mercury 90HP inline 6 s/n 0a149573 Charging Problem

[Wills Mercury]

Ok. I just got a new (to me) 1985 Arima Sea Ranger with a 1985 Mercury 90HP inline 6 s/n 0a149573. It starts and runs easily. Boat has Perko switch for batteries 1 and 2 at stern. Boat has perko switch and isolator for battery in bow. Motor is really clean under the cowl and looks to have (1) Switch box replaced (black potting) and another looking original (amber potting). Starter solenoid looks a bit corroded and rectifier looks newer (black potting). Problem is charging. I put my digital volt meter on each of 3 batteries and all are 12.4 volts running. I rev it up a bit and same voltage. I start motor with perko switch on 1 &2. 12.4 volts. I move the Perko switch to 1, then I get 12.4 volts, I move the switch to 2, then I get 12.4 volts. The volt meter on the dash reads approximately 11 volts. My shop manual will not arrive until this Saturday. Any advise on using the multimeter to test the stator and rectfier would be much appreciated. Also what other things that I should look at to make sure is connected... Thanks All...

[boats.net]

Run it on only one battery and put voltmeter on that battery. Monitor battery voltage while running at about 2000 rpm's for a couple of minutes should see battery voltage slowly increase.

[Wills Mercury]

Thanks for the advise..! I'll try that right when i get home from work on Friday.. and report back.

[Wills Mercury]

I think this is good news...

Ok. So the results were (1) battery 12.0 volts before starting motor. Running at idle 12.1 volts at around 700rpm. Running up to 1500 rpm, I got 12.8 volts and at 2000 rpm, I got 13.0 volts. I'm not sure if this is good or bad. I'm used to an alternator running 14 volts from idle to top rpm. Any thoughts...?

[boats.net]

That's good, alternator is charging battery. I think it had a 9 amp alternator it's not much.