Where does this electrical box go?

Depending on your installed electrical load you can go with a modern electronic voltage regulator (what I did) and the MAD bypass or go with one of the 1 wire alternaters and larger capacity, any case the MAD bypass is highly desirable!
As mentioned above, just a more modern DIN radio and hopefully an amp. I would like to keep the under hood loser to stock at the moment. No one wire Alt. The upgraded VR can wait at the moment.
How is the MAD by pass "Highly desirable?"
Or let me out it this way.
How many amp gauge fires have YOU personally seen? Actual view, not heard, or my buddy's friend and I read somewhere....