Welcome, Carlos, to the club.
You're problem may be the wiring of the OE wiring to the 10SI/12SI alternator, if this is the choice of model.
On the original VR connector, jumper together the two inner terminals and jumper together the two outside terminals.
The connector at alt should be swapped, meaning from the 10DN connector, blue wire and white wire are swapped places.
An adapter from 10DN to 10SI/12SI can be purchased from an aftermarket vendor or make jumpers and use shrink tubing to insulate the set-up.
If you used a CS series alt, their is a separate hook-up.
Moved your thread to Electrical as there is a thread about wiring in this forum, you might do a search.
This thread may explain and answer your questions. Use a 3-wire hook-up.
http://www.camaros.net/forums/19-electrical-wiring/105756-alternator-conversion-do-not.html