How do you wire a alternator?

Usually, these things are made so you can't mess it up by "keying" the connection. I'll assume the connection is broken since your asking. the positive (+) output (usually red) is plugged to the Positive side of the automotive circuit and the Negative (-) output (usually black) is connected to chassis ground or the negative side of the automotive circuit.

If its not clear what side is positive and negative, you should take it to a professional that will do a good job and has more knowledge.