93 Trans-am voltage problem

A friend of mine has a 93 Trans-am that has a voltage drop problem. Voltage drops below 12 when the car is warm and the ac is turned on at idle. He had a 108 amp alt. from autozone on the car. We found the correct 124 amp. alt. but the car still has the same problem. I'm wondering if the cooling fans are creating a short. Anyone had a similar problem or got any ideas?
Thanks for your time.

I had that same problem with my 92 and all it ended up being was a bad altenator... Your pully belt has enough tension in it, right? Sometimes if they are loose or worn out it could cause a problem. Donno what the odds are, but I've seen it...

its the LT with the sidecaps also right? remove the bolt from the plastic sleeve, take the sleeve off. on my sisters 97 and my 97, the sleeve was hiding the major corrosion on the wire. cleaning it off made my sisters car work! that simple :/ that is, if it isnt the tension..etc

Does the voltage go above 12v when you rev it with all the accesories going?