Voltage ups and downs: regulator, brushes, other?
When I turn on the ignition without starting the engine, the in-dash voltmeter reads about 10 volts. Then I start it, and after maybe five seconds the voltage goes up to say 14.5 V.
I believe the voltage is bouncing suddenly from about 10 volts to about 14.5 volts. The headlights and panel lights go bright suddenly and dim suddenly, staying one way or the other for a half second or a second or two seconds.
I think there is some sluggishness designed into the needle of the voltmeter, and I see it moving slowly between 10 and 14.5 rather than jumping suddenly, as the lights do.
After the car warms up, the voltage doesn't change as often. The needle stays near either 10 or 14.5 for longer periods. After it gets even warmer, it is near 10 volts most of the time. Eventually it goes into the red zone below 10 and the red warning light comes on.
When the car is parked, the alarm goes off spontaneously sometimes, with the lights flashing and the horn honking.
The battery is only a year old, but the car was laid up with other problems and was driven very little during that year. So I am not sure the battery is in top shape.
I had a mechanic test the thing in a hurry. He did not disconnect the battery cables. He said the battery was okay, but that there was some problem with the alternator.
Can you say what is probably wrong with the alternator? If I just have to open it and replace something inside, I would rather do that than spend $160 for a new or reman unit.
Certainly I would rather spend a few dollars on brushes if that is the only problem.
1995 Buick Park Avenue Ultra, L67, VIN 1, 160K miles