Alternator?

It may be a little new for this site, but I'm sure its all the same. I have a 1978 daily driver Plymouth Volare Station Wagon and it has stopped charging the battery and is running off the alternator. When i disconnect the positive from the terminal it stops running, I was told that it should continue to run. on the alternator gauge it reads towards the D. and I have tried 4 different used alternators, help me please! I need to Drive!

New Alternator maybe?


Nick