ok so i just finished completing my build on my car. i drove the car for like 4 days and all of a sudden my car started sputtering, when i would do anything more then feather the throttle. i noticed that the voltage was low and dropping and dropping.went down to 9.9. so i figured it was the alternator because there was a big stereo in the car before i owned it and it seemed like it was crapping out anyway because it didn't really charge the battery all that well. anyway, so i go out and buy a new alternator and i installed it. so then i fire it up and it's reading 13.3 volts which seems good. then it starts dropping off again. and it would go down to 12 even. then when i started going from a stop then it would go back up to 12.5 but it won't go any higher then that, when it should be running between 13-14 volts. i noticed that the sputtering decreased alot the higher the voltage got so i know the sputtering is due to the voltage. so i though it was the stereo maybe shorting out or something so i disconnect the stereo at the batter terminal. and it still won't go above 12.5. so it seems like the alternator is just keeping up. so i think that something is drawing power pretty hard, but i don't know what it could be or if that's the problem. what do you guys and gals think??

Check the voltage on each of the wires on the alternator. They all should be near the battery voltage while the engine is running. If you find one that isn't then that is the place to look for the trouble. You should have around 14 volts coming from the alternator while the RPMs are around 2,000.

You may want to have the battery checked also to make sure it is in good shape.