If the ground wire from the battery to the frame melted, and it's a 6 ga or larger wire, you have a dead short somewhere. In a large conductor, the only one being the positive cable. Assuming your starter is working, it's not going to be in the starter, or it wouldn't work.
I'd follow the positive lead from the battery, to the solenoid. and from the other side of the solenoid to the starter, looking for a cut or wear point. Finding none, pull the battery leads off the solenoid and check for a short to ground from either of two large terminals. Or, the two large cables touching each other at the solenoid.
Reasoning is that the ground wire is a large wire, can carry a lot of amps--probably, if melted, pulled 100 amps or more. The only other wire capable of carrying that much current is the positive cable. Any other wire shorting would melt before the heavier ground wire.
Make sure the hood or battery hold down isn't somehow touching the positive battery terminal, that could also do it.
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