Hello,

Tried previously posting in a thread, but got no suggestions..figured I would try once again. Thanks in advance:

Hi All,

New to forum...been lurking since I got my 1982 300SD a few months ago. Great forum, very helpful, thanks all! This is my first MB and my first diesel, but I am learning a great deal here!

I am experiencing battery drain/non-charging. The battery light has been coming on intermittently since I got the car.

Long story below, followed by what I've done (if you just want to skip to #1 below)

I was told by PO it had a brand new battery. No corrosion on terminals. When the problem was first experienced, I removed the alternator and had it bench tested at the local parts store. Checked out OK. Upon re-installation, the problem went away for a while...then, it came back. Once again going on and off at different times. I did notice it seemed like the light would flash when going over RR tracks, etc. I then began to experience a no crank situation (the car would eventually start after 2-3 no cranks). Upon a closer inspection of the alternator, I noticed the plastic mounting clip on the voltage regulator was cracked on one side. I figured this may be the cause of the non charging and the flashing of the battery light, so I changed the VR (I also cleaned the alternator harness at that time). I charged the battery and everything was great...for a few weeks. Most recently, the battery light would glow dimly on upon start up and occasionally shine bright all during the same trip. I ended up getting stuck at with a dead battery at Circle K.

To the best of my recollection, here is what I have done:

1. Changed voltage regulator

2. Had alternator bench tested twice (both check OK)

3. Had battery tested out of car (check OK)

4. Had charging system test at local auto parts store with the little hand held unit they use (battery check OK, alternator test bad at only 12.06V - although the car was not really warmed up and the guy was kind of in a hurry)

5. Did the ground terminal/ammeter test for drain with engine off: 10mA (approx, using cheap multimeter) which I assume is the clock. Also did the test light/ground terminal check and couldn't see any noticeable drain.

6. Cleaned engine ground to body contact(the twisted cable). Was unable to remove contact from motor for cleaning because it needed a special wrench.

6 1/2. Checked belt deflection (approx. 1/2" w/ thumb pressure) and visual inspection of belts (1035mm belts look almost new)

7. Most recent voltage tests (after 2nd removal of alternator for bench testing and full battery charge):

Across battery, engine on at idle: 12.4 (No increase at approx 3000RPM)

Across battery, engine off:12.55

Also performed alternator harness test from post #3, got battery voltage at both red wires (with neg. lead on voltmeter ground to body and pos. to one wire at a time). Did not however perform test on blue wire yet.

I took it on a ten minute test drive and was still getting a dimly lit battery light.

Battery light is off when ignition off, comes on when ignition on, stays on when running, will vary from dim to bright. Had occasion periods during trouble shooting when battery light would stay off when engine running and everything would appear to be normal.

Please advise if this post is too long or confusing, this is my attempt at being thorough.

Any suggestions welcome! Thanks!

You have a bad connection/lead from the alt to the battery.
I have had the same. All your tests dont show much as they are not done while a good load is on the system. I replaced the wire from the alt to the battery & it fixed the problem.
There is regularly threads on this same problem.

__________________
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

Just an update: Picked up a new alternator harness/cable, replaced wire from alternator to junction, initial test drive successful, no battery light.

Doesn't this electrical stuff just drive you nuts?
I've had trouble on and off for years. Think I put in 4 alternators. After each installation things were fine. Last week it went haywire again. As a last ditch effort before sending the car off to the electical boys, I changed the bulb ( battery warning light ) in the dash. Light worked, put voltmeter on, and car was charging.
That was an easy fix, but I thought everyone who suggested it was nuts because car always worked with a new alternator.
GOOD LUCK!

__________________
1984 MB 300SD Turbo

Layback40 had the right idea. Wiring will ohm out okay if you have all but 1 stand of wire broken. Doing a voltage drop test will reveal high resistance with current flowing - something a resistance check requires none of. Corrosion in the wire could have contributed - peel the insulation 3 or 4 inches and see if the copper has turned green or is white with powder.

__________________
Thanks,
Mark in NC

"Spark plugs?...We don't need no stinking spark plugs!"
1985 300SD "Der Silberne Schlitten" 420,000 mi


Wish these were diesel:
2003 Ford Club Wagon 130,000 mi