Wire from altinator get hot and melts the plastic on the fuse box as well as the fuse itself. the fuse is a 140amp that is bridged in the fuse box going straight to the pos on battery.the fuse does not blow just melts the plastic. just changed alt because would not start or batt would charge. what could cause this?

Besides double checking amperage output of new alternator, that it isn't running over recommended amperage, I'd check and feel all cables feeding current for weak spot, as well as clean connections well. Don't forget to look real close at any ground cables as well, when they are bad, it can also cause arcing and high amp draw.

There is a short circuit at some place in the car cabling its technical see an electrician dont try yourself

Overcharging, get alternator checked