Motorcycle Repair: electrical issues with my 75 honda cb500t, regulator rectifier, field coil

Question
I recently purchased a fine looking '75 honda cb500t, and started on my trip
home.  After 10 minutes of riding, the bike began to putt-putt, and eventually
lost power.  I tried to start it up, but there was no juice.  I tried kick starting
it, no luck.  I took it back to the shop where I bought it, and they told me that
the stator was bad, and that there was a short.  No problem....right?  Wrong!  
3 weeks later these mechanics can not identify the short.  The core problem
they tell me is that the bike is now sending a charge to the battery(with the
new stator they put in), but the voltage never goes higher than 12.5 volts
even when they rev the engine.  They say they usually get 13 or 14 volts when
the engine is revved.  I have been without my bike for 3 weeks now, and it is
getting old.  Can you help?

Sincerely,
Dave P

Answer
There are only three parts that can go bad in these charging systems...the stator, the field coil and the regulator/ rectifier.  If you changed the stator and it's still acting, I'm guessing that wasn't the problem.  You can check the resistance of the field coil and check the coil to ground and make sure it's not shorted to ground.  If that looks good, the only thing left is the regulator/rectifier but you can put 12 volts directly to the field coil and if the voltage at the battery jumps up to over 14 volts when you rev the bike up, it's probably the regulator.  I guess there are a number of connectors that can go bad too.  I've seen a number of them melt and don't make good contact so you might want to take a look at each of them and look for indication that things got hot.  

Good luck
Rich