Last night I started the car before driving 7 miles back to my house with headlights on. The car('78 240D) started up on the first bump. The battery light comes on rather dimly and fades in and out for the first three miles of the trip. The light goes out by the 4th mile. When I get home I plug my volt meter into the cigarette lighter and it reads 12V with the car off. I start the car and it reads 12V with no battery light on.
This morning I check the voltmeter and it reads 12V with car off. I turn the key to the glow cycle and voltage is 10.5 until she starts on the first bump and then jumps up to 12V. I figure the alternator must be doing something since the glow plugs usually cycle for another 15 seconds after starting. This is not the updated relay with afterglow. I went ahead and tightened the alternator belt a little to see if I'd get a higher reading in voltage, and there was no difference. The belt wasn't all that loose to begin with. I ran some errands, and started the car three times with no drop in voltage. The battery is only about a year old. Any ideas? thanks

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'81 300SD

Hey,

I had the exact same problem. I was dicking around with my 240's electrical system and killed my regulator. Here's what I did to test and successfully resolve.

Test to see if the battery is being charged with the engine running: Run all the electrical accessories (hi beams, etc) and let the car idle. Come back in 30 or 60 minutes (in your safe neighborhood). Turn the car off, then try and turn it back on. The starter should have very little to no power.

If this is the case-- and your alternator isn't making bad sounds or such, and is spinning, the voltage regulator is likely NG.

Two screws should be holding in your voltage reg on the rear side of your alternator. Take the little guy out and replace it.

Edit: Hey, I just noticed you live in Alameda. I lived there for the 1st nine or so years of my life. Should still be safe neighborhood!!

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1982 240D 4spd, 327,000mi

To check the alternator take your volt meter ground the neg. and touch the pos. on the large lead coming out of the back of the alternator with the engine running you should have charging voltage 13.5 or more volts. If you have 12v or less you may have a alternator problem. Form here move the battery iwth the engine running and make sure you have 13.5 or more volts. If not you probably have an regulator problem. Not sure how right on I am for MB but all my old Mopar stuff worked like that

Clean all electrical connections especially the earth strap ones. You need to remove the connections, clean the surfaces & then replace, not just a wipe over.

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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

Some info is missing here.

When you first turn your Key on did your No Charging Light go on indicating that the Light Bulb is OK?
After your Enigne is running is the No Charging Ligh on?

If your No Charging Light is Good but you are not charging some members have said the No Charging Light may not come on if one or more of the Brushes in the Alternator are worn too Short.

If the No Charging Light does not come on when you first turn the Key on the Bulb may be burned out. Without a good Bulb in the circuit you will not charge.

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84 300D, 82 Volvo 244Gl Diesel

Diesel911,

Isn't the battery light next to the high beam indicator the no charging light? It came on last night when I started the car, and just barely lit up this evening when I started the car and then went out when I left the driveway. I'm going to clean some terminals tomorrow.

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'81 300SD

make sure you pull the harness out of the alternator and clean the spades... that's what it was on my car... oily dirty connector.

At least the Bulb is OK.

Terminal cleaning is always a good Idea. Also about under your feet on the Drivers side (US) under the Car is the Ground stap from the Chassis to the Engine.

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84 300D, 82 Volvo 244Gl Diesel

Thanks for the input guys. I cleaned the brushes on the regulator and now I'm back up to 13.5V . It's always good to check in here first rather than panic and run to the pic n pull and start pulling parts.

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'81 300SD

Is there a reason the ground strap is bare wire? It seems dirt and oil residue can get in between the wire strands thus reducing continuity. Would it make sense to really clean it good and wrap it with plastic wire covering?

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Brad
1981 300TD - daily driver
1963 Chevy II
2001 F-250 7.3 Power Stroke

All of the Factory Ground straps I have seen on all the Cars I have owned have all been that flat sort of braided Wire with no insulation.
They are not insulated because there is nearly no danger of completing a Circuit when you are using tools around them.

I have seen the work literally packed with Oily dirt. The problems that have an effect on conduction of current mainly have to do with the contact areas where they Bolt up. Paint, Rust and other types of corrosion inhibits conduction.

The other Ground Strap issue I have seen is when the Woven/Braided Wire section simply get eaten up by corrosion or some other chemical action.

I am not sure but the way Ground Straps are constructed (flat and made of a bunch of tiny wires woven together and un-insinuated) may be due to that fact that they are most often short and need to be more flexible than The (+) Cable to your Starter which by necessity needs to be insulated and are usually longer and have a longer length to flex over.

I am not sure a short Battery Type Ground Cable mounted in the same place would hold up. Over time flexing the wires might break them.

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84 300D, 82 Volvo 244Gl Diesel