Lazy alternator light

[raueda1]

Per the subject - when starting the alternator light usually rarely goes out by itself after engine starts, especially when cold.  If I goose the throttle a bit it will go off.  Occasionally it will come on at a stop light but then goes off immediately.  Otherwise electricals seem fine and battery stays charged.  This is a long standing issue but I never bothered with it since it didn't seem to have an real effect.  Is this a know thing, reason to be concerned or sign of impending doom?  Advices appreciated as always!  Thanks and cheers,

[rumb]

Probably worn brushes in alternator.

[Neil4speed]

I might piggyback on this one... I have a 1977 6.9 and having similar syptoms.. at a stop, I have a light that disappears once throttle is applied or at cruising speeds. I believe to start at the voltage regulator/brushes as well.

How difficult is replacement of the regulator 1197311028 /removal of the alternator to do so? I see it on top, so it is visible and should make things a bit easier... Is there a way to test the regulator before going through and doing this? The alternator A0061547202 AL115X isn't obscenely expensive, but would prefer to go the easier route first if possible.

[rumb]

The VR/brushes are held on by 2 screws, though removal of alternator is prob in order to make easier.
I recently rebuilt my 6.9 alternator and it needed a new bearing also.  post #257 https://forum.w116.org/test-drive/my-6-9-s/msg157504/#msg157504

[Neil4speed]

Thanks sir, really appreciate the support - as always!

[raueda1]

Thanks folks.  The alternator is a newish Bosch replacement obviously replaced shortly before I got the car, it's clearly not a rebuild of the orig and certainly not the proper red 6.9 unit.  But I've got a low mileage 6.9 spare in all my junk so I guess I'll just swap that.  Now I guess the question is whether it's worth getting that one preemptively rebuilt first.  I have no reason to think there's anything wrong with it and I'd rather not spend the $$$.  OTOH......  Thanks again and cheers, 

[rumb]

Rebuilding is not expensive, mostly labor.  The only thing you prob need is VR/brushes, but also check if where brushes ride is still good.  I had one that was all worn out there.  I also found a bad bearing after it was taken apart. I think I have an extra bearing somewhere if needed.

Extra work to find original VR,  as new one is not identical if you are a purist.  The rubber boot is also hard to find exact replace, though subs are out there. Again I think I have a spare.