Did I fry my truck?

[Mike Bradbury]

Your battery should last longer than three weeks before it dies. Maybe there is a short somewhere that was slowly draining the battery.

On the cables sounds like pos. might of slipped, or rotated on the battery post and contacted metal like the fender or a bracket, maybe even the other clamp. Batteries have 700 to 1000 or more cranking amps in them the only thing that will melt a cable like that is if they get crossed or shorted. There isn't a wire under the hood that can sustain that kind of amperage for very long, so I doubt it was a pre-existing condition. Might have been a crack in the insulation of the cables and +/- made contact.