No idea what may be causing the short, but start with "what you did." You may have mis-wired someting OR THE NEW ALTERNATOR may be defective. Disconnect it.
Let's get some definitions:
"Cranking" or "cranking over" or "turn over" This means the engine rotates when the key is twisted to start, powered by the starter motor
"Fire".....Means try to start, cough, buck, possibly run for a few seconds
"Fire and run" means start and remain running not necessarily "perfectly."
NOTE If the engine won't crank, check for the dreaded SEAT BELT INTERLOCK and you should bypass it. When it trips it interrupts the start circuit which energizes the starter relay
This is the seat belt interlock reset box, mounted on the driver side fender apron
1974 duster seat belt interlock module removal
It has two "yellowish" wires, you want to splice them together.
I'm sending you a PM
