Starter lug melted

[karb]

49 cub let me cultivate a little before dying suddenly. Noticed the starter spring was stuck inward, and glowing orange!
Replaced starter switch, and it fired right up. Finished cultivating, parked her. Hour later she barely can turn, and I mean barely. Put it on a trickle charge (6volts still) for whole day, and nothing has changed.
Yes, the positive is grounded on the box, I'll change that tomorrow, but are there other things for me to look for?

Thanks for any help guys,
Karb