cranked her up early morn for a 300mi drive... stopped for fuel 190mi out, she wouldn't crank, got a jump and drove rest of the way non stop, pulled up, parked turned her off and attempted to restart... got nothing. jumped her over and drove 300mi without turning her off. Next morning - nothing... pulled battery returned to Interstate Battery Dealer, tested good, chargered for 2hrs, still good, they say, check alternater, returned home and placed battery on slow charge for the night. Question... why would car run 300mi distances with faulty charging system? If car will run for long periods, alternator is charging to some degree? why dosen't battery take charge generated by alternator and hold it enough charge to provide ample, sustainable and reliable cranking amps?
Car calls for 55amp alt, how does a 80amp alt benefit my situation... should i up grade? Thanks guys.

Once started, diesel will run till its out of fuel. One of the best things about them. Of course, lights are handy to have. I've started mine and pulled the battery out to start another car and driven the diesel home.

Is the alt charging? Is the belt loose? I'd start there

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95 E300D working out the kinks
77 300D, 227k, station car
83 300CD 370k, gone away
89 190E 2.6- 335k, no more
79 VW FI Bus- 145k miles, summer driver
59 VW Beetle ragtop- 175k miles
12 VW Jetta- 160k miles

Car will run forever with a faulty charging system. There's no connection between the charging system and the operation of the engine.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

When I first got my 300D, I was driving it to a friend's house about 20 minutes away. The radio started getting fuzzy and the headlights were incredibly dim, but the car didn't miss a beat. As soon as I shut it off, dead. Next day, jumped it and drove it on a dead battery to my mechanic who diagnosed the issue.

It's most likely the alternator, or the internal voltage regulator brushes are too worn.

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Never be ashamed to ask for help.

1985 300D
1987 300SDL
1970 Jaguar E-Type OTS
2002 Dodge Intrepid (Traded In)
2011 Ford Crown Victoria

I agree with Tanksowner.

However, if that doesn't do it (i.e. alternator check out ok), then the next place would be to look for a draw. A few years ago our 300sd kept losing charge despite a new battery & good alternator. In the end, I chased down a draw from the power antenna. It had enough juice to turn on dome lights/exterior lights etc, but never enough for cranking the motor. BTW, if this is the case, chasing down a draw is fairly straight forward (even for the less electrically inclined people like myself). Keep us posted.

Enjoy

http://www.peachparts.com/shopforum/diesel-discussion/331626-how-many-you-have-driven-without-alternator-battery.html

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1982 300GD Carmine Red (DB3535) Cabriolet Parting Out
1990 300SEL Smoke Silver (Parting out)
1991 350SDL Blackberry Metallic (481)

"The thing is Bob, its not that I'm lazy...its that I just don't care."

If you want, you can throw parts at it until you are blue in the face. It's your wallet. However, if you would like to really find out quickly what is wrong with it you will need a multimeter. With the leads placed across the battery, and taking readings in Vdc and Vac, with the engine running, you can almost immediately determine what is wrong. Anything else and your just guessing.

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Sam

84 300SD 350K+ miles ( Blue Belle )

I drove my car for over a month with out the alternator charging the battery.....one day is was just dead....got a jump.....and I came home....my problem....I put a new connector on the umbilical cord on the rear of the gauge cluster....and forgot to put the alternator pin in the connector.....

When you turn the key on your car does the charge/battery light illuminate? If that bulb is not lighting it will not charge the battery..


http://www.benzworld.org/forums/w123-e-ce-d-cd-td/1329121-battery-light.html

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As stated above, mechanical diesels will run without a functioning electrical system once started. Troubleshooting battery and starting system problems is pretty tough without a multimeter. Fortunately you can buy one good enough for that purpose from Harbor Freight and other sources for around ten bucks. A battery with a good charge on it will show a voltage around 12.5 volts with the engine off. Once started, the alternator should put out around 14, a bit less if there are other electrical loads present and the engine is at idle. Load testing a charged battery will tell you if the battery is still good. This requires a load tester, which is a different tool, but many parts stores will load test a battery for free.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

My 350SDL seems to be experiencing the same thing. I just replaced dash lights, and after reinstall, alternator seems to not be charging. Wife drove the car to Atlanta, and it sits there dead as I write this. Headed over today to take a look at it, but is there a diagram showing the alternator pin/connector?

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Mine: 1987 MB 420 SEL - 62K (Dec 2019)
Mine:1991 MB 350SDL - 244K (Aug 2011)- Totalled 9/14/2016
Mine:1981 MB 300SD - 326K mi (July 1997)-sold
Wife's: 2008 MB C300 Sport - 92K mi (April 2009)

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Car cranked, but just to get the car from my wife's workplace to a basement garage here in Atlanta. No gauges or lights. I need to get the car home where I can work on it in the comfort of my own garage...

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Mine: 1987 MB 420 SEL - 62K (Dec 2019)
Mine:1991 MB 350SDL - 244K (Aug 2011)- Totalled 9/14/2016
Mine:1981 MB 300SD - 326K mi (July 1997)-sold
Wife's: 2008 MB C300 Sport - 92K mi (April 2009)

wiring to the alt is really simple, just two wires really... small one goes to the resistor/battery bulb and the big ones go to the battery.
I've built a jumper with a 40 ohm 10 watt resistor to clip onto the small post for alt testing in the field.
that and a jumper wire to VERIFY ground is to the alt case, and it's a sure test of the alternator.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

I appreciate all replies/help... First thing this morning with Battery fully charged and installed, she cranked, drove to auto parts store, checked charging system - battery/Alt test SAT. Pls note, lights, air, nor radio were on during the check. I did not use any auxilaries at all today and I cranked/started her with no problem several times. I failed to mention in initial post, at 25mi from home a loud buzzing noise sounded, coming from something behind the instrument cluster, lasted about 30 minutes and stopped. Radio started cutting out and in... during return trip, at night the dash lights were initially bright and then became dim, this went on until I arrived home and parked. Now I'm thinking... which function is causing the drain on both battery and Alt? Lights, Air, Radio/antenna, cluster instruments? I have the volt meter and will test charging sys with each function on individually and with everything on high at once. Anyone been here before? Thanks.

I had a parasitic draw before, but it was steady which made it easy to find. I know glow plugs stuck on suck enough juice to overpower the alternator. Maybe look into that.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

That sounds very similar to what I was dealing with on my 'SD. For a brief while I installed one of those Priority Start batter saver things; it worked reasonably well by extending the battery drain intervals. However, in the end, the best thing I did was spend 30mins to isolate the draw from the fusepanel. I used a simple test light attached to the battery negative after disconnecting the negative lead, and touched every fuse (do a google search for instructions if needed). The one that lit up was the one with an open short. Once I narrowed down where the short was, I looked at the fuse panel guide to isolate which accessories it runs, and individually unplugged those, then retested with the test light, until I found out it was the power antenna.

edit: make sure you don't have any open doors, since those will mislead you as open shorts. If the hood light works, unscrew the bulb for this test also, or else it will appear as an open short.

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"Time's never wasted when you're wasted all the time"