shorted diodes should not cause massive AMOUNTS of current to flow through the system, and likely not even AC current as the diodes only serve to cancel out half of the phase on the three coils, should one or two or even all of these short out it would lead to almost no voltage as the phases of the three coils would cancel out.
Short of aliens I would suggest checking the wiring underneath/behind the fuse boxes, or a wire that overheated melted and shorted to ground. just keep looking for something this big you should know when you find it, you'll likely find some burned chunk.