Check the terminal voltage at the battery posts with the engine at fast idle. It should be 13+ volts, minimum. Against a fully charged battery with the engine at a fast idle, the voltage should go to 14.5 or slightly more.

Yes, the generator need to be polarized. Even if it's already polarized, doing it again won't hurt anything. With the engine stopped, use a short jumper wire to connect the BAT and ARM terminals of the regulator together momentarily- - - - -half a second or so is plenty. You'll get a pretty good arc- - - -don't get a case of the vapors- - - -that's normal.

Now, with that little chore out of the way, go ahead and check the generator for voltage and current output. If you don't know how to do that, find somebody who does. Relying on the dash ammeter to give an accurate measurement of charge/discharge current is not sufficient. That meter is a WAG at best.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!