If the car has a bad battery the battery will not charge just becaus you put a new alternator in try raplacing the old battery.
Repair the alternator to battery connections or replace the battery.
you need a new alternator.
If it the 3.8........start by disconnecting the battery. Then remove the sepertine belt. On the back of the alternator, there is a red cable and a plug. Undo those. Then there is only 3 bolts. Two in the front, one on the back.
Only if the old battery is defective
My advice is to charge the battery with a battery charger before starting the engine. You will be putting a heavy load on the alternator if you allow it to charge a dead battery. This could damage the alternator.
You have a bad alternator.
Not likely, but running the engine with a dead battery can damage some alternators. Always fully charge the battery when installing an alternator.
To wire a 1995 Pontiac Sunbird alternator, first ensure the battery is disconnected. Connect the large battery terminal on the alternator to the positive battery terminal using a thick gauge wire. Then, attach the smaller wire (typically a plug for the voltage regulator) to the alternator's terminal, ensuring a secure connection. Finally, reconnect the battery and check for proper charging operation.
Normally it means the alternator is defective.
Alternator is not putting out a charge.
An alternator is designed to keep a fully charged battery at peak level. It is not designed to charge a dead battery. Installing a new alternator on a car with a dead battery can in some cases ruin the new alternator. Fully charge the dead battery before starting the engine.
It could be your alternator is going bad