Voltage drop, HELP!!

Hey everyone, I'm driving a 96 Tahoe 5.7 and I've been having charging issues with it lately. For starters it has a brand new red top Optima battery and I just put in a brand new 100amp Bosch alternator.

The problem I'm having is that the voltage drops when I turn on the heat full blast and have the headlights on. If the headlights and heat are off it's fine charging @ 14 volts. If I hit the lights on it's okay, but as soon as the heat goes full blast it drops down to battery voltage and I start to hear a squealing form the belt.
I figured at first that okay I have a weak alternator, thought it's starting to slow down and seize that's why I hear the squealing of the belt spinning faster then the alternator. But I changed it out for a brand new Bosch today and still same problem so now I'm stumped.
Could it be a bad ground?
Any info would be greatly helpful and appreciated. I would like to figure this out before I start work again because juggling between heat and headlights is brutal in early morning traffic!

A full speed heater function draws only 20A. That should not be an issue. If it drops that much the culprit would probably blow a fuse. But since your belt sqeuls I would suggest the belt is stretched or your tensioner is defective. Ensure clean firm connections. Go to a local parts store and have them load test the battery and alternator seperate to eliminate a defective new battery as well. Only other thing is a different diameter pulley on the alt. but that is a longshot.

I was just reading online about others that had the same problem, they say an old belt and tensioner could be the issue?

If you let your tensioner snap loose into to the free position with no belt then it is probably busted. Should cost less then $100 for a new complete tensioner and belt

Alrighty thanks. Im going to buy a new belt and tensioner today hopefully it will solve the problem. I also hope they will take the alternator back i only used it for less then 5 minutes

---------- Post added at 05:08 PM ---------- Previous post was at 03:15 PM ----------

Yup it was the belt and tensioner. Problem solved. But they didnt return the alternator but oh well lesson learned. Thanks for the replies sunlitcomet!

your welcome.

good call Jon, shit i would of never of guessed. lol