Recently the battery light was coming on randomly in our '86 BMW 325es. Once, while the light was flickering, the car sputtered out and stopped running while my wife was driving and another time the car wouldn’t start after stopping for a breakfast sandwich after driving my 30 minute commute. We had the alternator checked and then replaced even though it checked out OK because they told me that was the only thing that could cause the issue. Only several weeks into the new alternator, the battery light will randomly flicker, the radio cuts off, the AC fan will surge and blow very hard in quick burst, and the lights will brighten randomly (it looks like I am flashing my brights at everybody). Does the alternator have a voltage regulator in it or is there one located somewhere else in the car and could that be the cause? What else could be the cause? Will surges in electrical power damage the vehicle badly?
Your voltage regulator is in the back of your alternator. It costs $28 on line, and is easy to replace with just two screws holding it on. Cheaper to try another one than to have a mechanic even look at your car.
However, I am not at all certain that is the problem. This model car has a rather colorful history with charging systems. BMW tried two different alternators and apparently several voltage regulators through the years. The alternator you put on was almost certainly rebuilt, so it is only as good as the rebuilder, and may have been rebuilt on a Monday or a Friday ;-).
First thing is to figure out whether this alternator is supposed to ground through the bracket or whether it is supposed to have a ground strap. You can tell by looking at the mounting points. If they are all supported in rubber, you need a ground strap. Actually, it cannot hurt to add a ground strap if uncertain.