You should have an electronic voltage regulator. The way they work is one wire with full battery voltage (Blue?) goes to one of the field terminals on the alternator. Another wire (green?) from the other field terminal goes to the voltage regulator where it goes through circuity to produce a variable ground to very the field strength to modulate the output of the alternator.
If the alternator was changed recently the wrong year alternator may have been put in. older cars (69 and older????) used a ground field alternator. Rebuilders are short on round back alternator cores and use a square back core but they ground one of the terminals to convert it to be a functional equivalent to a round back.
to test the alternator remove both field wires and check for low numerical ohms on each field terminal to ground. any reading other than "OL" or what ever your gauge reads when both leads are not touching each other indicates the alternator might be bad.
you said the blue wire is fried, from where to where? can you see its entire length?
if it is in a wiring harness and it melted / fried it is very likely that other wires in contact with it are also fried.
What ever happened suggests you have a direct short somewhere. if you have an electronic choke look at that wire as it might have fallen off and is shorting to the Manifold
you will have to trace out the problem there is no magic bullet we can share. every failure with these old cars is unique to your car.
