normally goes dead on the panel and the engine won't start or stop when that breaker is operated is because the ground wire to the panel, which is probably about a No. 10 black wire, is laid down on the ungrounded up stream side of that 50 amp breaker. When the breaker is opened the ground is removed from your control panel as well as removing the ground to the engine. With no ground the panel and everything else like the start and stop solenoids won't work. When your wire was pinched either the ground load was passed to a smaller ground wire which overloaded and melted taking the other wires in the bundle with it or the pinched wire, which I assume was a Positive wire, shorted to ground and overloaded and melted also taking the other wires it in the bundle with it. That's my guess. If the burnt wires were not bundled together and were running separately then all bets are off. Good luck.