Battery dies when car is running

I have a 91. Recently put in a new alternator and battery. Battery died. I thought that one of the parts was bad out of the box and replaced them both again. I still have the same problem. I was told the voltage regulator is built into the alternator, so that eliminates that part. What else could it be? Someone said that their may be a fuse between the alternator and the battery, is this true? What other parts could I look at for the problem. This is my friends car, and she is going crazy (and taking me with her) without it. Thanks...

I looked at a wiring diagram and there is a connector for the alt behind the battery and there is a fusible link behind there also.
Justin