the 1404 is a Caterpillar (not 'Mitsubishi') motor designation, sometimes referred to as a "Hercules" motor in other brand of forklifts [some Daewoos had the same setup].
It is a pretty simple wire harness and does not have much in the way of bells and whistles. does the fuse blow as soon as you turn on the key" or as soon as you put it in gear? or as soon as you turn on the lights?
Have you installed any lights or other components that run wires up the overhead guard? have you taken a 'good eyeball' to the wires where they go into the distributor?. Those are the first places I would be checking first.