well depending on which 'hot wire' your speaking of , if it is the one that goes to the control circuits and not the starter wire (which is a negative feed from the keyswitch through the instrument cluster) then i'd say you have a dead short to the frame between the control wiring and fuse panel. That is if it is not blowing any fuses and just burning the wire.
Which terminal on the starter is it hooked to? it should be on the same post as the battery cable. Are all connections isolated well from each other on the solenoid?
also note:
The alternator does pick up its positive feed before it gets up to the keyswitch and instrument panel so you might want to consider having that alternator checked out and check the wiring from it as well. Make sure the charging circuit wire to the battery is not grounded anywhere.
To verify the starter just remove it from the truck and bench test it.