Flickering alternator light

[GSpreeman]

My alternator light flickers at low rpms. As I rev up it gets dimmer and flickers less. Is there a DIY that I can do to clean the brushes or something. I'm between jobs and don't want to drop any $$ into the car unless absolutely necessary and I don't think that the car is ready for a rebuilt alternator...yet.

[island911]

Replace the brushes and/or brush springs. Thats what it sounds like it needs.

[jk911]

I would take early -s mans advice and clean all the connections on the blue wire D+/61 and or put a 68 Ohm 5 Watt resistor across the warning lamp $0.30.

refer to my earlier post !

[Ove]

GSpreeman,
island911 is right. On my BMW 1600 2.2 the charge light started to glow weakly on and off. At first I thought it was a relay. Replaced it, but the charge light was still glowing. Pulled in at a gas station, 2 o'clock at night to check the brushes on the alternator. The brushes were so worn down that the brush springs could not push them down to make contact. The battery was dead.
Obviously there were no way to get new brushes in the middle of the night, the gas station didn't even have a battery charger!
Solved the problem by placing a piece of gravel between each brush and brush spring. No problems since. When I replaced the alternator 12000km later it was still working with the old brushes...
Don't get me wrong here, do it right and replace the brushes.
I think there is a tech article here at Pelicanparts on how to remove/replace the alternator.

[s_wilwerding]

I have a followup question:

When I start my car, the alternator light is on. When I tap the gas, it goes out and stays out. Any ideas? It doesn't seem to be a big deal since the battery holds a charge just fine.

[twin plugged targa]

Anyone with suspected alternator problems- learn by my missfortune (with the empahsis on lost fortune )
Check that the fan shroud has not been overtightened once upon a time and the casting is cracked causing the fan to touch the shroud and give impression of failing alternator (replacements of which we all know are not cheap!)
Evidently this is a common fault- according to Vertex but one I have never heard mention of on this board.
Still, something to check!.
Hope this is of some help
rgds Ben

[Ove]

Steve,
The alternator light goes on when the charge from the alternator gets below a certain point. This could happen for various reasons: 1. There is something wrong with the charging system
2. The engine is running at very low RPM
3. The point at which the alternator warning light goes off is set too high (never seen this happen, though)
If your engine is running under, let's say 800 RPM just after you start, it will not charge enough to get above the point at which the light goes off. When you tap the gas, it charges more and the light goes out. On my BMW 02, the light occasionally comes on when I stop at traffic lights and it gets low on RPMs (when it's cold).

[s_wilwerding]

Originally posted by 911777
Steve,
The alternator light goes on when the charge from the alternator gets below a certain point. This could happen for various reasons:
2. The engine is running at very low RPM

If your engine is running under, let's say 800 RPM just after you start, it will not charge enough to get above the point at which the light goes off. When you tap the gas, it charges more and the light goes out. On my BMW 02, the light occasionally comes on when I stop at traffic lights and it gets low on RPMs (when it's cold).

This sounds like the problem. My car always kind of sputters for a few moments after starting - once it's running strong there are no problems.

Thanks!

[ischmitz]

Originally posted by GSpreeman
My alternator light flickers at low rpms. As I rev up it gets dimmer and flickers less. Is there a DIY that I can do to clean the brushes or something. I'm between jobs and don't want to drop any $$ into the car unless absolutely necessary and I don't think that the car is ready for a rebuilt alternator...yet.

I have the exact same sympthoms on a 74 911. The light keeps glowing slightly even at higher RPM's yet charging is fine. If idle drops beyond 800 RPM (cold engine) the light comes on full but switches to glowing once I feather the gas. An in-car test revealed that the alternator still charges but not with it's full rated current. In my case this seems to be caused by one open rectifier diode that causes AC on D+.

My alternator has 6 main rectifier diodes and two isolation diodes. The brushes were fine.


D+ at 1000 RPM