alternator issue

What is your question?

I replaced alt 5 weeks ago. About 5 days ago the battery light came on. I noticed that if I rev car up to 4-5k rpm the light goes out. I replaced alt again and light went out, but after 10 miles or so the light came back on and car died. I was able to get it home and I put back in alternator #2 and I am able to make battery light go out as long as the engine is run up to 3k rpm or higher. Is there a relay or fuse etc that could be causing this. I have not made any modification or anything to the car. Thank you I appreciate the help.