Ok so I have a wierd screeching sound coming frOm under my hood, I did the 3G upgrade and it was making a slight screech then it would go away. Now it's loud as hell and won't go away and get louder when I get on the gas. However it goes completely aaway when I take the negative cable off the battery!?!?!? HELP!!!!

 

Road noise?

 

1) Don't remove battery cable with engine running. Can cause voltage spikes damaging electronics.
2) I suspect belt is slipping, wrong belt, too loose or wore out.

 

its a belt. if anything else was making that sound,, well, it wouldnt be making ANY sound by now.

 

Taking the negative is a way to check the alt is good too is it not? No it's not road noise. This is at idle in my driveway

 

Belt problem then
Put a wrench on the back of ALT it will magnetize when working

 

I would say you should also load test your battery, sounds like it is drawing a lot of load from your alt., very possible it is fine but could possibly have an internal problem.
I have a 94 Mustang with a 460 swapped in but I retained the original Alt. and serpentine belt, it also squeals when first started but goes away after a couple of seconds.

 

with proper tension and a good belt, there should never be squealing......

 

So can anyone determine why when I take off my NEG battery cable it stops squealing? But as soon as it touches the post again it starts again?

 

the battery loads the alt. making it harder to turn, thus slipping the belt and squeling. i reccomend tightening the belt, or replacing.

 

Thank you, this makes sense
To me now.

 

you may even need to add a second belt to help... the 3G alts are harder to turn because of the higher amps they put out.

 

I only have a single belt pulley though, you have a part number for a double from autozone or oriellys? What else what I need to change besides that? Freaking casing is so big it wedges between the motor and the bar that goes to the top bolt. Really tight fit

 

Defective alternator bearings can cause screeches, so can the bearings found in idler pulleys used with P/S and/or A/C.

 

I do not have p/s ir AC