The electrical in there is terrifying. Setting that aside, it looks like your rafters - those aren't trusses - are transferring the load to the ground at the vertical studs. I'm having a hell of a time identifying a "conventional" top plate, unless its that thicker board it appears they carved a bird's beak into - rather than beaking the rafter as is more typically done now, and the rafters either butt into, or are nailed into the studs from the side. WOuld have greater confidence if I could walk around inside for a few moments.
Assuming that's the case, and that you have adequate overhand outside (not sure the strength or direction of your prevailing winds), you could simply remove the next to top board along the outside on the long wall, install hardware cloth, flashing to protect the now exposed top wooden edge of the cladding from moisture, etc. If you don'd want to rip out a board, and don't mind the damage to the existing structure, I'd use a big drill with a keyhole saw blade (like you use for putting holes in for door knobs) on the highest thin board you can safely access from the inside, centered between the studs, sized not more than 1/3 the width of the cladding board, again, centered. Then attach hardware cloth to the inside and call it done. If those cladding board are 8" wide, you are talking a 2 1/2" hole saw bit, probably two holes between each stud. Don't forget to paint/seal the fresh cut before attaching the hardware cloth.
No, I'm not a builder or an engineer. I did just build my own barn to FL hurricane code, had to read quite a bit before I was confident in proceeding.
