The way the MAD thing works out "in the end" is that the original black and red end up being a parallel feed, and the black no longer carries alternator current. There are several ways to do this. The MAIN thing is that you have some sort of fuse protection so that a massive short won't burn things down
Couple'a versions:
You need a fuse from the battery feeding the rest of the car so that a big short anywhere will pop the fuse or link. The way the original is set up IF YOU ADD a jumper FROM the alternator to the battery, depending on how (model year changes) the fuse link is set up, you can end up with NO fuse protection IF THE ALTERNATOR diodes short. And by the way this DOES happen.
