[Mg-t] Generator revisited

[Andrew Moyce]

A few weeks ago I posted about my TD generator.  It's a rebuilt Lucas,
about a year old.  The ignition light wouldn't extinguish and no charge
on the ammeter.   The testing from the shop manual points to the field
coils (shorting the field and output terminals together, then measuring
voltage between them and ground yields only about 1 volt, up to about
1500 RPM.)
I had an older generator with intact field coils, so I swapped bodies
(with field coils) reassembled with the new armature and brushes,  and
got the same result.
Weeks passed, with other cares getting in the way.  I reassembled the
rebuilt in its own case and put it back on the car.  Start the engine .
. . ign light stays on.
I left the engine on while getting tools together to take the generator
off, and then  noted that the ign light was now off. Increasing RPM
showed positive movement in the ammeter, so all is well, right?
Turned off the engine and restarted . . . ign light stays on for about 3
or 4 minutes, then all seems right again.
Tried a third time and the light won't go off, though revving the engine
makes it glow brighter, which suggests that the generator is talking to
someone.

Questions:
What's with the intermittent charging (fan belt is not slipping)
Could both field coils be bad?

This all started after the front generator bracket broke, which caused
torque on the old generator, wore the bearing and caused the armature to
rub against the field coil (visible damage inside the casing.) Could
this be happening again, if the replacement bracket isn't perfectly
lined up?

I don't want to rebuild/replace the generator and have the same thing
happen next year.

Andy Moyce
52 TD