Alternator won't charge my car?

I've tried everything I can possibly think of. First, I replaced the alternator. No go. Still died. Okay, so I replaced the battery. Still died. Okay, so I take it to my mom's friend (mechanic for 38 years), and he noticed my wiring is really corroded. He finds three electrical shorts and fixes them. I get a new battery and alternator again. Still died. Now we get a new ground cable that connects to (I think he said the air conditioning) to draw power from the engine. Still died. He has a tester (2 of them) and it's always saying that the alternator is indeed charging. But clearly something else is wrong. The car used to indicate some signs before it died, like the speedometer moving a lot, or the radio turning off while driving. But it just died now and showed NO signs that it was going to die. But it did. The car never turns off while driving, only once I turn it off, then try to turn it back on. Nothing is working, I really need help, please! When I try to turn my car on all I get is clicking and the lights dim. We thought maybe something is draining the battery, but that doesn't make sense because when I drive, the alternator should charge my battery, but it clearly is not and I don't know why. By the way, I am pretty inexperienced with cars and mechanics, so if you have an idea, please explain it to me as simply and easily as possible. Thank you for your help. If you need any other details, email me at ysakuragirl@gmail.com (It's a separate email account so I don't get junk mail on my real account.)