Got a dim alternator light on the 300D Wed evening, naturally while taking a "shortcut" at night out in the country. I'd been cussing the headlights (more likely my aging eyes) because I was having trouble seeing.

Made it, finally, and drove home. Light went completely dark on the highway.

Thursday, on my way out of town on the way home from work, I realized my headlights were VERY dim (didn't show up on the tailgate of the pickup in front of me) as dusk approached, and when the ABS light came on when I touched the brakes, I made a U-turn and headed back into town to the Autozone (this is a small town 35 miles from home) and bought a new battery. The old one was probably OK, just dead, but it wasn't the correct size anyway. Don't like autozone batteries much, but it got me home.

I'd already ordered a new voltage regulator, but didn't pick it up til today, and won't get it in until tomorrow evening -- major "whoops" at work will require my presence tomorrow.

Question is, will the new regulator fix this, or is it likely I also have bad diodes in the alternator?

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Alternator should be easy enough to check. What's it sending to the battery while the vehicle is running? How about with a load? If you're not using the correct battery (too small), maybe starting is taking all she's got?

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1982 Mercedes-Benz 300CD
1982 Mercedes-Benz 240D - stick

PS:

I'm sure you're ahead of me on this but here is what I know:

1. I had a similar experience and the new VR worked for one week and then the symptom appeared again. Turned out that one of the diodes on the alt was shot. Got alt rebuilt, installed a second new VR and presto.....all was well.

2. Should be able to check the output while car is running. Anything in the 12's and its not well, but the mid 13's (if I remember right) show that the alt is working and sending a charge to the battery.

Don

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DAILY DRIVERS:
'84 300DT 298k (Aubrey's)
'99.5 Jetta TDI IV 251k (Julie's)
'97 Jetta TDI 127k (Amber's)
'97 Jetta TDI 186k (Matt's)
'96 Passat TDI 237k (Don's
'84 300D 211k Mint (Arne- Undergoing Greasecar Conversion)

SOLD:
'82 240D 229k (Matt's - Converted-300DT w/ 4 speed

I'm hoping it's just the voltage regulator, but have a feeling it's the diodes. Same thing as the 220 when I re-did that one, although I expect this alternator to be a bit less expensive -- all I got back on the 220 was the case, the rest of the guts were bad!

I'll check the voltage when I get the regulator in tomorrow, have to get to this one from underneath I think.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

It's normal for the ABS light to come on if voltage drops below 12 volts if I recall correctly. I once drove about 40 miles home with zero battery voltage and a failed alternator. Only things noticeable were the windshield wipers didn't work (sucked cuz it was snowing moderately), and it didn't idle quite right because of the computer. Ran fine though.

Yeah, the idle was bumpy and the AC compressor was clicking on and off constantly, but otherwise ir ran fine. Wasn't for the stupid time change I'd have made for home, but driving on twisty roads at night with no headlights is for teenagers.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Finally got the new regulator in. Knew it was the brushes when I took the old one out, no spring pressure!

Old brushes were only about 3 and 4 mm long, new ones more like 15 mm!

Nice to have headlights, and I can drive it to work now rather than Big Blue -- much better milage!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!