Disconnect the battery immediately - if a wire is getting hot there's a serious fault - a fire in the engine compartment is the next stage.
The car has fuses to prevent too much current, heating wires and a resulting fire - the current in the hot wire has found a way back to the other side of the battery without going through a safety fuse.
Summon a motor electrician or wait arround and summon the fire brigade.
Take care...
Peccavi
November 2009