Agree. Alternator Warning Light Bulb is one of the first things you check after maybe the voltage across the battery. If that bulb is out - replace it right away. I just loosen the plastic underdash cover to easily reach the bulb.

Essentially, check all the obvious things first. Bulb, VDC, Alternator Belts, grounds, connector to Alternator, VAC. Kinda the vital signs of the charging system. Then you should have the info to diagnose.

__________________
Codifex
1981 240D ChinaBlue (Got her running with a donor engine.)
1983 300DTurbo w/sunroof.
1984 300TD manual sunroof. (Electrical Gremlins)

could someone please detail this procedure? where to connect +dmm lead and -dmm lead? car running or not? do i need to disconnect anything before this procedure?

before i start replacing parts...i've been having these same symptoms and it passes all checks but now i'm to the VAC check. the battery tender/desulfator i installed last week has gotten the car started every day since, but there's a definite drain, even after driving the car. thanks.

should i just go ahead and replace the brushes just because, and see if that fixes the problem?

__________________
1982 300sd from craigslist $800 greased on one tank with NO CONVERSION in the Hot Texas Sun. (currently dead & awaiting engine damage investigation and/or longblock swap)
new daily: '03 vw 5speed jetta tdi wagon. bagged&chipped

Sorry I copied it from My Notes. While the Engine is running Meter set to the lowest AC Voltage Range; pick a Meter Probe and Put one on the Positive Battery Terminal and the other Probe on the other Terminal.

__________________
84 300D, 82 Volvo 244Gl Diesel

i'm getting 30.1 when my dmm is set to 200vac mode.

what might that mean?

__________________
1982 300sd from craigslist $800 greased on one tank with NO CONVERSION in the Hot Texas Sun. (currently dead & awaiting engine damage investigation and/or longblock swap)
new daily: '03 vw 5speed jetta tdi wagon. bagged&chipped

Please remember I copied that info from someone else. I wish there was a better explination for the test.

When I did the Test if I put the +probe on the +Terminal and the -Probe on the -Termanal I got 13.3 vac (with Harbor Freight Meter set on 200 VAC).
When I reversed the position of the Probes I got Zero VAC. And, I am having no dead Battery or charging issues.

I also checked My Van Alternator using the same method and got 30.8 vac and when I reversed the Probes Zero vac. I am also having no dead Battery of charging issues with My Van.

So I would say that you passed the test if you get 30.1 vac with the Probes in postion described.
I found the Meter Instructions and am going to read them to see if the Probes are supposed to be in a differnt Socket when you do the VAC test.

ADDED: The Probes go into the same Sockets as with VDC measuerments. However, it said if you want to read lower than 200 vac to change the Selector Switch???? So far I cannot find any lower VAC voltage than 200 vac.

__________________
84 300D, 82 Volvo 244Gl Diesel

I found a better descriptiion of the VAC Test but still cannot find how low of a range the VAC Test is supposed to be done at. They still say just to set the Meter on the lowers VAC range.

Test - Ripple
Voltage Ripple test on automotive alternators
Test - Ripple
"ALTERNATOR - Ripple Voltage Test Using a DMM
The Alternator produces AC voltage and current. The battery requires DC voltage and current to charge properly. Diodes located within the alternator change (rectify) the AC to DC. However, a small amount of AC can still be present and no harm is done. Problems can develop when alternator diode faults permit unacceptable amounts of AC to pass into the vehicle electrical system.
1. Set the meter to read “AC” Volts (lowest range) .
2. Connect the black COM lead probe tip to the battery negative post.
3. Connect the red Volts lead probe tip to the battery positive post.
4. Run the engine at 1500 RPM.
5. Turn ON the high blower and high beam lights.
6. Your meter reading should not exceed .09 volts (90 mV) AC.
High ripple voltage readings imply faulty diode(s) which can cause:
· Undercharged battery.
· Stalling.
· Rough idle.
NOTE: If your meter reading exceeds 90 mV AC, use an ADL7100 labscope or equivalent to verify that ripple voltage spikes do not exceed one volt peak to peak"

OK I tried raising the Engine rpm to 1500 and there was no change in the reading.

__________________
84 300D, 82 Volvo 244Gl Diesel

Would some of our Members who read this and have the Harbor Freight Volt/Ohm Meter please do this VAC test on their Cars that the know the charging system is working OK on and tell us what VAC you get when you do the VAC Test?

I have a Harbor Freight Cen-Tech 7 Function Digital Multimeter with the Backlight.
Model/Item 92020 (in small numbers on a tag on the Back.)
200 vac is the lowest AC Voltage setting.

Would one of our Members also do the same test with a high quality Multimeter.

__________________
84 300D, 82 Volvo 244Gl Diesel

Finally working on this again...

I've pulled my voltage regulator, but now I've lost confidence it's the source of the problem. It looks very similar to the one depicted below, except: The brushes, while much longer than 1/4 inch, are 1/8 to 3/16 inch uneven, and don't emerge from the plastic housing at right angles. Most alarming is the "bottom" of the brushes (closest to the top and the camera in the photo to the right) -- each brush "barrel" has a jagged, uneven metal protrusion. They look like old solder material, broken off.

Trying to decide whether to replace the entire alt. at $77, or just the V. R. at $41.

Any thoughts?

Thanks!!

The jagges protrusions are on the bottom, as the part is installed, and while I can't see into the hole in the alt, there doesn't seem to be anything loose where the protrusions would sit.

Y not go for the saab junkyard upgraydd with two d's for a double dose of output

__________________
1982 300sd from craigslist $800 greased on one tank with NO CONVERSION in the Hot Texas Sun. (currently dead & awaiting engine damage investigation and/or longblock swap)
new daily: '03 vw 5speed jetta tdi wagon. bagged&chipped

Is it potentially harmful to drive my car without the V. R. installed? (W/o headlights and most accessory power draw)??

Thanks (and apologies) to all...

It WAS a stuck glow plug relay -- I must have been really stupid that day that I "eliminated" that theory.

My alt/V.R. is fine. No idea what those "jagged protrusion" are or why my V. R. looked so gnarly and wonky, but it's all back together and charging the battery, as long as I remember to unplug the gp relay...

__________________
1980 300TD

would the jagged stuff be like brush material that has worn and then accumulated on the other side of the brush?