This.
I had a weird electrical issue with my '94 Grand Cherokee - auto antenna would go up and down, radio would go in and out, one rear turn signal work work interimittently, other things, it seemed completely random. A shop spent 3 days trying to run it down with no luck. When I finally got feed up with it, I ripped into it. I found that when I "repair" a loose heat shield underneath the unibody, I ran a self-tapping screw through the floor to hold the heat shield (and keep it from rattling) and ran it right into a wire bundle on the inside of the cabin below the carpet under the rear seat. There was a section of wire bundle that, over about 6 months, had slowly shorted out and heated up to the point of melting the wire cover. I replaced a 12" section of wire bundle - there was about 10-15 wires in that section of the harness.
Long story short - if you know that there was mice in the bike chewing on stuff, it seems fairly reasonable that this sickness could be caused by a section of wire harness being mangled enough to ground out against other wires. It could be nearly invisable depending on where it is.
With all the parts that have been thrown at this with no resolution, I'd start looking hard at the wire harness - which is a project that would involve stripping the bike down to the frame.
Just my .02...