1986 Chevy Truck truck won't run when I disconnect the batt

Well if it wasnt the alternator before, it is now. It is very very bad to disconnect battery cable when vehicle is running. The alternator full fields and you can blow it up real fast. Check for voltage at the back of the alternator at both the red wires. If you have voltage at both these wires then your alternator is bad. If one of the wires does not have power then this is your problem. Hope this helps