I suffered thru a similar gremlin several years ago....after weeks of trouble shooting and replacing main fuses - As I was moving my 2007 Venture from the garage to the driveway at night - I saw a very brief spark coming from the below the fairing and next to the left shock - and then the fuse blew. After weeks of trying to track down this bugger - it showed itself to me. I got a flashlight and immediately saw where the headlight wire had become pinched and only caused the main fuse to blow when I turned tightly to the left - causing the exposed wire to short. After a quick and proper repair, replacing the main fuse - I never had a problem again. I determined that I actually caused the problem as I had opened the fairing to do some "add on" work. When completing that job, I didn't check my work and I had caused the wiring harness to "work free" to the point that the headlight wire was being pinched.
The smallest of issues can drive you nuts - and then to figure out that I caused the problem...and heeerrrr's your sign!