Hi. I've read the threads on similar issues with interest. On my 2001 Night Train, the 30 amp circuit breaker will kill the bike sometimes when I hit a bump in the road. It resets immediately upon turning my ignition switch off and back on, then I can restart and I'm on my way. It doesn't happen with every bump. The other day it happened twice in quick succession on mild bumps. I spent the next 150 miles hitting every bump and pothole I could find and of course it wouldn't happen again.
I have replaced the breaker with a new one. Obviously I have some kind of short. How can I help my mechanic narrow down the troubleshooting.

 

What parts of the bike wiring does that breaker protect? You probably have a chafed wire that is only occasionally making contact with something, eg where your wiring goes through a hole, such as the rear fender to the lights. Another possibility is a loose connector or ground. These things are often mechanical, which your mechanic should know! By that I mean that something is loose, or making a poor contact. It is probably something very simple, when you find it!