im gonna take a radom shot in the dark that still needs to be addressed.

have you checked the engine to frame ground strap?

try running a ground wire from the alternator straight to the negative post on the battery and see if that affects anything


if that doesnt chime back in and we will dig a little deeper

 

Where should it attach on the alternator? I have the positive to the battery and two wires in the 3 pin connector but none of them are grounds that i know of

 

on these trucks the body of the alternator is the ground itself, which is why i said make sure the engine ground strap is still in good shape and attached to the frame. if you run a purpose ground from the alt to the battery just put the wire on one of the mounting bolts at the alt. and run it straight to one of the negative battery terminals.

 

Okay, i tried it. Still putting out 11.75 volts

 

what is the voltage at each battery while disconnected ?

what is the output voltage of the alternator with no batteries connected ?

 

Batteries both read 12.5 right now, it wont start until i put it on the charger but to check the alternator output without batteries i should just unplug the positive to the passenger battery and go from the alternator to ground?

 

Another thing, it ran fine for like a month when i got it. Then when i changed the alternator the first time it ran fine again for another couple weeks until it got to the point that its at now

 

AZ alternator is crap. Many failures. Get a delco or motorcraft from rock auto. Also, 12.5 v and the new batteries wont crank without putting a charger on??
That is odd. Did you buy these new batteries or the previous owner? Check them with a conductive battery tester to test the cranking amps. 2 new batteries should crank well without a charge.

 

How are your battery cables.