I was replacing the ground wire on my alternator when I noticed there is a small green wire (maybe 18 gauge) coming off of the positive terminal that goes nowhere - its broke off. I cannot find a broken wire to reconnect it to anywhere. Any ideas where this should be connected to? Also, I see many discussions about upgrading a 240 alternator to an internally regulated one, what about the 280?

The little wire probably once went to a noise suppression capacitor. You can get a generic replacement one from your local auto parts store. The body of it screws to the back of your alternator, and the little wire goes to the (+) output post.

You can upgrade a 280 to an internally regulated alternator if you want. However, there's nothing wrong with the external regulator. The #1 reason why the 240 owners upgrade is that they want a beefier 60A output.