Toyota Repair: 1989 toyota fuse link blowing problem, amp fuse, 40a

Question
1989 toyota pu. 4 wd, 5 speed manual, no ac.  r22e engine. started blowing  40 amp fusible link(labeled AM1).  it blew first time and i replaced it.  truck ran 1/2 day with no problems. Battery is 2 yrs old. when fuse link blows, truck dies and will not turn over. no obvious arcing evident any where on visible wiring and no electrical burn smell when it happens.

Answer
The 40amp fuse gets it's voltage from the 80 amp alternator fuse, the current flow is then to the ignition switch, since this fuse blows while driving the "ACC" and the "start" position of the switch can be excluded as the cause, the current then flows through the clutch start cancel switch to ground. Since the 80 amp alternator fuse is connected in series with the 40 amp fuse there must be a current draw of more than 40a but less than 80a or the alternator fuse would blow also so it can't be a direct short to ground just an excessive current draw, I'm looking at the wiring diagram and can't see a reason other than there may be a problem with the alternator or it's wiring.