Interesting electrical problem

[Paulcet]

I rode about 80 miles to my mom and dad's last Sunday for Mother's day.  I had my 11-year old son on the back.  After about 70 miles, everything quit.  At 75mph.  In the left lane.  Quick head check to the right and I pulled over, clutch engaged for part of the time hoping it would restart.  But there were NO lights, indicators, nothing.  I suspected the fuse, but what would cause it to blow?  I didn't signal, flick highbeams, nothing.  Just steady state running then "Aw, crap!" 

Sure enough, it was the fuse.  I looked at all the wires I could get to without removing the gas tank or tail plastic, and didn't see any problems.  I replaced the fuse and checked for lights.  All seemed to be fine.  Started it up, expecting it to blow.  All still seemed fine.  So we rode the last 10 miles to Mom's.  On the ride home, everything seemed to be fine for another 70 miles when I stopped to fill the tank.  After filling up, the first try to start resulted in a very discouraging "wump".  Hit the button again and it started.  Once I got out of the little town I turned on the highbeams.  5 miles later the tachometer was dead.  A few more miles and the speedometer was intermittently dead.  The last mile home everything was pretty dim (at about 9:30pm).  Battery voltage was only about 7-8 volts.

I put the battery on the tender for the night.  Next morning I checked the voltage with RPM at 5000, and got nothing more than the battery's own 12.7 volts.  I then unplugged the stator connection, and saw the culprit:  One of the wires had been touching the subframe and wore through the insulation.  The stator was putting out the right voltage.  Diode check found one shorted diode.

So, I ordered a new rectifier/regulator.  Oh, and I left the keyswitch on all night and KILLED my battery.  So I also got the Walmart sealed battery to replace it. 

When I pulled the rectifier/regulator off the mounting bracket I found a spot where the epoxy potting material had burned.  So, my theory of the failure is this:  The short to ground on the stator wire caused a diode in the rectifier to short.  Then because of the diode short, the regulator got a 70 volt reverse-bias which sent it to silicon heaven, which blew the fuse on the way.

Got it all put back together tonight and it's good to go!

[scottpA_GS]

Great post  Should be VERY helpful to others trouble shooting electrical issues