The way they get re-wired the red and black form a parallel path. This does two things..........the new wiring sends charge current direct to battery, so charging current does not have to go through the bulkhead ammeter. This relieves strain on that wiring. Second, the parallel path means that the red and black, working in parallel, work as one big wire to feed current for the rest of the car.......headlights, heater, etc
Some guys don't like the way MAD does that and advocate simply jumpering from the alternator direct to the battery. That is OK, too, but it removes the fuse link protection........which is damn poor to start with
If you do that, I'd add a breaker/ fuse link to the new part of the circuit
