follow the system feed wire(the small one that hooks on the starter cable post) and look for bare or pinched wires until you get to the fuse. usually if the short is before the fuse there is a fusible link that burns in two. it sounds like your problem is on the backside of the main fuse though. i have seen the hot wire in the trailer plug short out and cause problems before. i don't recommend it but the only way i found it was put a paperclip in the fuse block and watch for smoke. with these new vehicles anything is possible it seems.
a wiring schematic for your particular vehicle would help you find the things that are powered from this fuse and narrow down your search a whole lot.
