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Lazy alternator light

Started by raueda1, 03 September 2024, 07:52 AM

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,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

rumb

Probably worn brushes in alternator.
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS
'21 E450 Cabrio

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
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS
'21 E450 Cabrio

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, 
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

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.
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS
'21 E450 Cabrio