Where does this electrical box go?

Do they not roll off the assembly line with a matching drive line that can handle the horsepower?
See the thing is, We know heat builds slowly, over time, and eventually melts something rather than blow the fusible link. For yours to fail under the dash first was not typical. You haven't stated the root cause of that overheating either.
My best guess ( where absolutely nothing was altered/added ) would be windshield wipers.
Never mind.