It was none of the above. The 1/0 Ga. Cable from the disconnect switch to the starter motor had a defective terminal. A 2/0 terminal was used on a 1/0 cable, thus did not fit as snuggly as intended. Even though the terminal was crimped and soldered to make up the gap, there was still wiggle room. Which thanks to vibration, it did. Thus, there was enough contact to make continuity, and if the batteries were charged to the max, enogh current would pass to start the engine
. But the bottleneck of the weak connection resulted in those frustrated elections having to do something, so instead of turning the starter motor, they heated the cable.
Lesson: unless you're in a critical have- to situation, use the proper size. In retrospect, 2 ga. cable would probably have worked better than 1/0 cable and improperly sized terminals.