Hello All, I noticed yesterday on my way to the mine that my headlight brightness is fluctuating. Not alot but enough that it's definitely noticeable. Seems to be the headlights only, not the fog lights. Plus it only does this when the engine is revved up, not at idle.
1) Battery is less than 2 months old. Tonight measured 12.8 volts at rest.
2) Alternator belt appears to have the appropriate tension.
3) Voltage regulator in the alternator is less than 2 years old.
4) When the engine is revved the voltage measured between 14.3-14.6. Is this enough of a fluctuation to cause my problem and how do I fix it? Any help appreciated. Thanks,JEFF

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1981 240d aka "The rust bucket"

sounds like a charging issue. Check the regulator also check your batt connections

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hum.....
1987 300TD 311,000M Stolen. Presumed destroyed

My wagon was doing that a while back, and it was the voltage regulator. I'd suggest pulling yours out and looking at the brushes.

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Mine does the same lately. I am already considering replacing the alt for peace of mind. Regular is next.

HOWEVER. Those are not my cause. Found out it was the headlight switch since I could wiggle it and things would instantly change. So it may not be your issue, but something to consider.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

Regulator is the most common cause.

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Gone to the dark side

- Jeff

like everyone else i vote reg. get a meter and check for a/c voltage.

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1996 s10 zr2 with a 6.5 turbo diesel
1996 c2500 suburban with a 6.5 turbo diesel
1981 300sd with a turbo 617
Monte carlo figure 8 car

The Below is from my notes of comments from someone on our forum:
ALTERNATOR DIODE check with volt meter
"With your meter across the battery, on Volts DC, you should read 12.5 - 14VDC

If not, set your meter to Volts AC and you should have a reading of ~100mVAC.
If the VAC is too high, then look for a rectifying diode failure. If VAC is OK but the VDC is not correct, then the problem is with the voltage regulator."

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84 300D, 82 Volvo 244Gl Diesel

Do you have a sound system? ;-)

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1987 300TDT - 195,000 (Original #14 head)
1993 190E 2.3 - 105,000
1981 300D - 250,000

thought diode was part of reg.

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1996 s10 zr2 with a 6.5 turbo diesel
1996 c2500 suburban with a 6.5 turbo diesel
1981 300sd with a turbo 617
Monte carlo figure 8 car

No sound system. I'll check the regulator tonight when I get home. Thanks.

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1981 240d aka "The rust bucket"

No, the diodes (9 of them), are on a board where the windings terminate. They rectify the alternating current (AC) into direct current (DC).

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

There are 6 of them to rectify the current to give the charging DC required for the battery & other things in the car.
The other 3 rectify to give DC to provide the excitation of the alt rotor. There is at least a diode in the reg to make it work, it cannot be replaced as an individual component though.

If your switch is good, you may have bouncing brushes or a bad brush in the alt reg. If that is not it, you may have a bad connection in the light wiring.

I once had a locust get into the alt & jam a brush. Ended up with a dead battery. Was I P#SSED OFF when I found the remains of it in there.

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Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

Mine did this when I bought the car, a new regulator fixed it. Brushes were fine.

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Gone to the dark side

- Jeff

Ok, I finally had a chance to install a new voltage regulator. It did not solve the problem. Battery is still charging ok though. So what is the next thing to check?
Also besides being a little annoying is it actually hurting anything that the voltage is fluctuating a little? Thanks

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1981 240d aka "The rust bucket"

sounds like you may have a problem with the alternator itself. the shaft that the brushes ride on could have some corrosion or be worn down. this happened to my 123 and i put 3 regulators in it until i pulled the entire alternator and took a look inside. shaft was filthy so brushes were only touching in a few places.

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1987 300D 180k
1985 300SD 330k Helga
1992 300D Lola 269k- Sold
1986 325 coupe Bessie >300k Original engine(ODO Broke) sold
2006 2500HD Druamax Linda- Tows boat and looks pretty in garage thats about it