I have a 85 firebird 5.0 305. I replaced the alternator and it was not charging my brand new battery. Checked it with a multimeter. I thought it was maybe a bad alternator so I bought another one and it is doing the same thing. Checked the grounds and they are good. What elnce could it be?

 

"Choke" light come on with key on and engine not running?

 

Yes it does

 

Does it go off when the engine begins running?

 

Yea it does

 

So, the main guts of the alt are at least mostly working.

What's the voltage on the big stud when not running and when running?

 

What big stud?

 

Where the big red wire goes.

 

Make sure that the alternator is connected to the block and therefore connected to the negative terminal of the battery. Also insure that the positive terminal on the alternator is connected to the positive side of the battery. If either side becomes disconnected while the engine is running, it will almost assuredly blow the diodes in the alternator, so never disconnect the alternator when the engine is running.
With the engine off, connect a multi-meter set to amps, between the positive battery terminal and the cables that are to connect to it. Note the amount of current and then trace down line by line what is causing this current. You can sometimes do this by having someone watch the meter while you pull each fuse one at a time.
It maybe simple such as the headlight motors are not turning off, or the light in the console box is not turning off, or the door switches, but with all the things people do to these cars, it may be a nightmare under the dash.

 

But shouldn't the alternator be chraging it around 14volts with the car running?