Don't feel bad: I got so frustrated trying to chase down the intermittent dead short in the 550 for my book that I bought a new harness instead(!).
It turns out, the PO installed a (stiffer-than-OEM) PVC jacket sheath over the main harness from under the tank into the headlight, and it kinked in the bend where it goes between the headlight and tank. Inside this kink, the sheath sliced (barely) thru 2 wires (Black and something else with Green/[faded stripe] on it) so when there was car-wash water collected in the sheath and the handlebars were turned left with the key ON, the main fuse would blow. Every time. When dry, no problem, except the electric start solenoid would not then work (probably the Green/something wire).
Then, some of the insulation would crack in my fingers when flexed. Time for a new one, then.