Another alternator not alternating

Yesterday the stock charging system quit working. Admittedly the previous owner hacked the wiring harness, but it was working. I have all new under hood harnesses ready to go when I pull the motor in a month or so. Anyway, the local parts store says the alternator is good. I swapped out the regulator as a crap shoot, but that didn't help.

With the motor running at 2000 rpms on battery I read the same battery voltage on the back of the alternator (Batt term to Alt Grnd). Same voltage (11.5v) at Batt Term to Field. With the car off, I read the same 11.5 v at Alt Batt to the negitive post on the battery and at Alt Grnd to positive post of the battery. The car instantly dies if I pull the positive battery cable while running.

This sounds like the alternator isn't charging to me but the store says no. What am I missing?

Thanks for the replies gents. Unfortunatly I need a little extra help since I'm not dealing with the stock wiring harness (or even color coded wires).

So... I have battery voltage across alternator ground to pos on the battery. That tells me the ground is good.

I have voltage from the + terminal on the altnerator to the Neg battery post, so the "hot" side of the alternator circuit is okay.

The problem must be in the wiring going to the "field" terminal going from the Alternator to the regulator.
Can anyone tell me what voltage I should see if I lift the "field" wire and measure field wire to pos or neg on the battery or what the field terminal on the alternator should read, referenced to the pos or neg battery posts(wire disconnected, car running)? Or am I missing something with this logic?

Remember I have a home made harness w/o the normal plugs or splices and all the wires are black... Can't wait to put the new harness in