Following up on this original post.
Generator stops with a red light alarm on Over Speed.   VR light is not lite when the engine runs.  Engine only runs for about 30 seconds, then stops.  Field Boost to VR is 11 volts, but no power voltage at all to MCB.  Book says to replace VR.  Did not fix the problem.  After another post I read, it recommended cleaning the slip rings and brushes.  I disassembled the unit and cleaned the slip rings with a rag and electrical contact spray cleaner, resurfaced the brushed.  After installing the brush assembly, I started the engine.  The light on the VR was lite up as it should have been.  Power voltage to MCB was 245 volts AC.  Seems to have fixed the problem.  Do you guys see this as a reoccurring problem after years of service on these older units?

Stopped by to check generator this week.  The Over Speed light was on again. Spent some time running a few test.
Field Boost was 11 volts. Switched the voltage regulator, made no change.  Check circuit on 0 to 4 through brushes read continuity, switched the control board after running more test 4 test, made on change.  Ran several other test from manual with no success.  Finally gave up for the day.  No more time left.  Put the parts back in place closed up the generator and tried it again.  It worked fine.  Light on voltage regulator on , voltage out put to MB was 245.  Stopped and started several times, set the exerciser.  Neighbor says there is a ghost in his house and it may mess with the generator.
Stating to believe him.  Wondering if there is a loose wire.  I tried to wiggle all connection I could when in there.  Working fine when I left, will look at it Friday after exercise time. Got any ideas, please share them.
What was the temperature and humidity?  My old (2006), now gone, 7 kW unit would get condensation or frost on the rings and fail to field boost.  I fixed it by installing an upfit kit.  It did not care that no voltage was being generated.  It would run fine with no voltage being produced.

Overspeed faults can also be due to bad ignition coils, the controller gets the speed signal from them.
What are the Ohms from the #4 wire to ground?  Yes, every couple years you may need to clean the slip rings.  This problem is made worse on days when the air temperature rise somewhat quickly and the cold iron of the rotor sweats.  If this continues to be a problem one solution is to install a continuous field flash kit.