Alternator not charging

I was driving and the battery and brake lights came on the dash. After driving for a bit the ABS light came on and the vehicle lost power and would not accelerate. Eventually it just stalled out. I boosted it with a booster pack and was able to make it home. I wound up replacing the battery with a brand new one and replaced the alternator with a refurbished one from a salvage yard. After installing both components the vehicle did the same thing instantly. I then purchased a new alternator and had my mechanic replace it. It was running fine for about 2 days. The minute I switched on the defroster the battery and brake light came back on. The vehicle was still holding a charge. After driving for another 2 days the vehicle stopped holding a charge again and eventually the abs light would come back on and the vehicle would not accelerate again. I checked all the connections, grounds and fuses. All where okay. What else can it be? I feel that something is shorting somewhere.