>>    What is a "weak" ground?
>
> We tested it with some electronic gizmo, but I forget the numbers and what
> they meant. I cleaned it up and the numbers got better.
>
>>    Gotta wonder why that particular spot got hot, though.
>
> I'm guessing that that spot was touching the engine block and formed a
> better path.

FWIW dept.: I used to do a lot of wiring of racers, trailers,  
and ORV's .  I like to see the return cable to be at least as
big as the cable(s) feeding into a compartment.  Translate
that
to mean: if I have a 4g wire feeding the starter circuit, I want
to see a 4g wire going from the block back to the battery.  If
other items ground through the engine - as opposed to having
their own return paths - (e.g. the alternator) then I install
a 2g engine ground.

Dale R.