I had noticed the battery light coming on at night, and early in the morning with my lights on. The light would go off, and I had no trouble starting, until this weekend after taking my wife and daughter out for dinner and a movie my car wouldn't start.

The next morning I pulled the old battery and had it tested. My battery was less than one year old, but tested bad. Replaced battery. Also, after reading several posts about changing out the voltage regulator, I pulled the voltage regulator (internal Bosch). The old voltage regulator brushes were wore down to nubs, so I replaced it with a new one.

With the new battery and new VR, I started it up, battery light came on at first, but then went out. I then drove around for about 10 miles with all lights on, AC running, windows rolled up and down etc. Battery light never came on, starts great.

This morning when driving in the battery light comes on again . As before, the light is intermittent. On the way back home this evening the battery light doesn't come on. I take it to the parts store where I bought the battery and they tell me that the charging system is not charging.

Do I need a new alternator, or did I somehow screw up installing the VR?

Thanks in advance.

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1989 300E
103,500 miles

1982 300SD
Sold but not forgotten

Did you disconnect the battery before replacing the Voltage regulator?

Also, you might check your engine to chassis grounding strap, near the starter, as this can give you charging problems.

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Sam

84 300SD 350K+ miles ( Blue Belle )

Yes, I had the battery completely removed while replacing the voltage regulator. Hadn't thought about grounding strap. How would I check it?

Thanks,

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1989 300E
103,500 miles

1982 300SD
Sold but not forgotten

Just physically check it to make sure it is attached securely. Mine was attached to an exhaust bracket that was loose and eventually caused starting problems.

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Sam

84 300SD 350K+ miles ( Blue Belle )

Haven't been able to crawl underneath to check the grounding strap, but I did get a voltmeter and checked battery voltage. With engine off, I read 12.6 V, started engine and read 13.1 at idle. Turned on lights, got about 12.9 , with AC about 12.5 (idle) 12.9 at 2000 RPM.

Do these voltages seem right?

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1989 300E
103,500 miles

1982 300SD
Sold but not forgotten

your voltage should be about 14.5 or so just after starting at an idle. your voltage readings are too low, you might have one diode burned out in the alternator. Take the alternator to a reputable shop or parts store and have them check it. Pep boys or O'reillys, autozone etc. will check your alternator for free.

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'83 240D 264k on 100% biodiesel/ 31mpg
83 300D 217K the $800 gem
'82 300D 267K the new WVO project car finished and driving for free
International tractor B275 on B100
Ford 555 backhoe on B100
Sargent 25 ton Rough Terrain crane on B50

Thinking the worst, I ordered a rebuilt 85 Amp Bosh alternator on EBay. If I have to go through the trouble of pulling it, I might as well replace it. Unless I can change out the diodes without pulling it,,,

Thanks for the help

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1989 300E
103,500 miles

1982 300SD
Sold but not forgotten

Yes, those voltages are low. A poorly grounded alternator, ie. ground strap, or a voltage regulator would be my first suspicions.

This can easily be checked with a good voltmeter. Check for DC and AC voltages at the battery and terminal strip using the battery as ground as well as the engine block. The presence of AC voltages indicate a diode problem. Low voltages indicate voltage regulator. If you get different readings using the block as a reference from using the battery as a reference, indication of poor connections or ground strap.

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Sam

84 300SD 350K+ miles ( Blue Belle )

for a quick check on the ground connection from chassis to the engine use a voltmeter with one end connected to the ground cable connection on the body and the other on a clean metal connection on the engine.Crank the engine without waiting for the glow plugs,that way it will crank long enough for you to get a reading on the meter before it starts. A significant reading on the meter is an indication of a poor connection in the ground circuit.you can then narrow it down by moving the test lead to either side of the connections until you find the one(or more) causing the drop. My $.02 Don

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Red Green "This is only temporary,Unless it works!"

97 E300D 157000 miles
87 300TD ?141k? miles

Thanks for all of the advise.

Finally got me a set of ramps so I can get under and take a closer look at everything. First thing I am going to do (after disconnecting the battery) is to check out the grounds, then pull the VR I installed to see if I might have not put it in right. If I can't find anything, then I have my new rebuilt alternator to install.

Any advice on the best way to change the alternator?

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1989 300E
103,500 miles

1982 300SD
Sold but not forgotten

I replaced my alternator with a rebuilt one, still getting the same voltages as before.

I spent a lot of time under the car with a huge light, and could not find a ground strap . The ground from the battery is attached to the frame in the battery compartment. I pulled that, cleaned, sanded, and di-electric greased it and put it all back together as tight as I could get it, but to no help.

Also, noticed that the alternator wiring harness was very brittle/corroded. I WD-40'd it and put it back together with lots of di-electric grease. Still looks suspect though. Could this be part of my problem?

Also, can you buy the entire wiring harness assembly from the battery to the alternator?

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1989 300E
103,500 miles

1982 300SD
Sold but not forgotten

After changing the alternator out this weekend, I kept driving the car even though the voltages were initially lower than advised (13 volts at idle). Car started up and ran fine. Today on the way home from work, I noticed my tach stopped working ( wasn't working when I first bought it, but I put the "fix" on it) thought no big deal. Then the fan on my AC got really low, again with so many CCU problems, I thought again no big deal. The battery light still wasn't on. Stopped the car at the Dentist to get my teeth cleaned . Came out and battery was dead.

From previous posts you may recall that I have already changed the Alternator. With my voltmeter I checked for AC voltages and read none. I put one lead on the positive battery post and one lead on the terminal block that the battery cable and alternator cable goes into and read about 5 volts.

Also I noticed when jumping the car off, there was a whirring noise in the trunk ( vacuum pump?) then all of a sudden all of my door locks popped open. The locks have never worked since I had the car.

Does someone have a photo on where the ground strap is located on an 82 SD? And does anyone have wiring harness between the battery and alternator.

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1989 300E
103,500 miles

1982 300SD
Sold but not forgotten

I'll send a pic of what I have on file, you can see part of the strap. It's the braided cable near the flex pipe. This is the new down pipe. Your tach problem may be a faltering amp.

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83 SD

84 CD

The grounding strap is a large braided cable that attaches to the passenger side of the chassis just forward of the starter. There is only one so if it is loose or missing, you definitely would be seeing lots of electrical problems.

I believe you can buy a new alternator harness from the dealer but a salvage harness in good shape would be your best bet, costwise.

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Sam

84 300SD 350K+ miles ( Blue Belle )

Uncle P, do you have a set of jumper cables handy? Connect one end to the battery (-) and the other end to the engine block somewhere. If there is no improvement in your "not-charging" problem, this may eliminate the ground strap as the fault source.

Just a suggestion.

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Gary

1979 300D