my 2002 325i bmw batery light comes on and off ? on 2002 BMW 325i

I have changed the batery and alternator, but the light still comes on and off?

Asked by for the 2002 BMW 325i
poss bad alt. were did u buy it and how long ago
i tested the Alt and its good also the batery is new ,one week old.the volt meter is showing that the Alt is 14.5 volts.