There's not much of a fuse panel on this (everything on one fuse) so it's hard to pull fuses and check. My guess is that you have wiring chafed someplace and it probably only shorts out under just the right conditions (turn this way, bounce that way). I would start looking at any wiring that isn't rigidly attached, like anything swaying in the breeze, as that is most likely to get chafed and have a short--stuff that is tightly held against metal is the next place to look.
Sorry, this will likely be tedious work, unless if you come across it by accident.
You could try examining the wiring diagram and try to disconnect everything except ignition, then start adding back in circuits... easy to describe, hard to do since there's no fuses to pull.