alternator: mitsubishi but not vr4 specific

[ercp98]

i have a 1998 full size montero. the A/T, Brake,battery lights on the dash turned on all at the same time.
after some research it boiled down to the alternator. so i took off the alternator and had it tested at auto zone.the alternator passed.
i reinstalled it but the volt meter says that the alternator is putting out 14 volts at idle. however with load... lights on. a/c on, radio on and trans in drive... the voltage drops to 11 volts. does this mean that the alternator is actually bad and yet passed the test?
i used both a volt meter and an alternator / battery tester to test the alternator and battery.

thanks in advance.

 

[alansupra94]

Voltage shouldn't ever drop that low. Is the battery okay?

Does the voltage go back up when you rev the engine?

 

[ercp98]

yes the voltage goes back to "normal" at about 13 volts. i dont need to rev the engine, but it helps. it drops like that when i am at a light waiting to turn green. i am guessing that the low idle, 750 rpm does not help. that is what i was trying to simulate when i was testing the truck in my driveway. but that is what the spec says the idle should be. however while cruising the voltage stays constant at about 13 (i am basing this on the dash mount volt meter). so at this point,am i right to think that the internal voltage regulator of the alternator is on its way out? because it cannot sustain voltage when there is high load ( lights on, radio on, a/c on, and trans in drive while at a stop light) while idling. battery is about a year old. i tested the battery while its out for voltage. it is at 12.5 volts. which i think is normal.