300SD Battery drain - help?
 

1981 300SD
315,000 orig miles

I've had 2 Indy's check for electric shorts and possible source of battery drain

we changed a faulty emergency flasher switch and old rear taillight connections...
and still can't figure this out.

Any suggestions on what to look for how to pin point are appreciated. I've had the 3yr old Interstate Battery checked and my alternator too and I'm told both are holding and charging ...but in the morning we have dead battery...

AA


..

1. Get your $$ back from the indy if they didn't fix the problem. Or pay me 1/2 price and I won't fix it either.
2. Connect your ammeter between - battery post and cable. How many amps is the drain?
3. IF you have a documented drain as measured by excessive amps, pull fuses until you isolate the circuit.
4. Identify then disconnect individual items (loads) on the circuit until you identify the problem.

Question: What specifically makes you think that the battery and alt are good? You need to be CERTAIN that both are good before looking for a drain. Lots more info available online but post back your findings.

good ideas but i would also do this

pull one of the battery termninals off place a test light between the terminal and the battery post -- if something is on in the car the test light will come on if its a dim light than the alternator diode tro is leaking voltage and draining the battery over night < having said that the diesel has a big amp battery so my guess its not going to be a dim light but maybe if battery is not real strong but under normal conditions starts the car --

sooo if you get a light when conecting the test light you can take one fuse at a time out of the fuse box and look to seee if light went out when it does, -

that is the circut that is causing the problem -- could be trunk light could be clock yea the clock could be somthing that is not r\urning off --

let me know if that works for you or if you need more info about how to do the test -- jz

I have been experiencing the same problems in my SD. Too soon to celebrate, but I think it's OK now. As has been suggested here, I disconnected a battery cable and put an ammeter in series. Found I had about a 1.4 amp draw for maybe 10 seconds and then the draw dropped to about 24 milliamps. Had read somewhere on this forum to expect the larger draw for a few seconds. Not really sure what causes it, but both my MBs do it. I pulled the fuse for the clock and the 24 milliamp draw went to zero. Assumed that there was no drain in my circuits. Had recently replaced the alternator, but tested it also. No leakage in the diodes. Put out 13.7 v when revving the engine. Took the car to Wal Mart and Auto Zone and had the battery tested. Both places said it was good. Kinda stumped. Finally I took the battery from the SD (one experiencing the problem) and put it in my300D. Sure enough, the D started experiencing low battery problems and the SD started today in 30 degree weather after sitting for 4 or 5 days. Put a new battery in the D and hopefully am in good shape now. Really not sure how that battery tested good both places, but it seems to have been the culprit.

It's the memory for the radio. Usually when doing this test with a DMM, you want to have the probes from the meter in contact with the post and terminal, then disengage the terminal. You won't see the transient spike then, and it could save you a fuse in your meter (or meter if it's a cheap one without fuse)

I WANT TO TRY THIS TONIGHT IF POSSIBLE....

IS THERE A SINGLE FUSE OR LINK THAT CAN BE DISCONNECTED/ PULLED

OTHER THAN UNDOING A BATTERY TERMINAL THAT WILL DISENGAGE THE

BATTERY FROM BEING ACTIVE?

I CAN FULLY CHARGE THE BATTERY TONIGHT AND IF DISENGAGE WHEN CHARGED

THEN ENGAGE IN THE AM.......IF BATTERY IS CHARGED THEN I KNOW I HAVE A DRAIN ISSUE..

IF BATTERY IS DRAINED THAN I KNOW I NEED A BATTERY..



.........

had similar problem of dead battery after car sat for a day or two.

turned out it was the trunk light... the wire near the trunk hinge was shorting against the hinge and turning the trunk light on when the lid was closed.

Austin, there is no fuse that covers everything. so you need to disconnect a battery terminal. Charging the battery over night is a good idea. Just a thought, is your trunk light staying on?

There are UnFused circuits that can go "Bad"
 

The Alternator Diodes are one example.
A Stuck Pre-Glow Relay is another.
(Either one of which will drain the Battery)

Schumacher Electric has a Tutorial Page that walks you through Automotive
electrics 101:
http://www.schumacherproducts.com/applications

These Two pages are my favorites:
http://www.schumacherproducts.com/applications/?id=0007
and
http://www.schumacherproducts.com/applications/?id=0014

I know that, on my 190E 3.0, I had some issues with the alternator. I bought it from Advance Auto (143amp) and I've replaced it 3 times now (this one seems to be working fine now, we'll see how long it lasts) and when the alternator would begin to fail it would show up as a draw on the battery when the car was off. First it was small but then it grew larger until the alternator was completely dead and useless. It was drawing near 5 amps from the battery. I actually drove about 40 miles on pure battery not even knowing the alt was gone. Luckily I realized it on the way home and ran in "power saving mode" lol.

It very well could be your alternator. The several times I had advance test the system it came back clear everytime, but with a substantial draw on the battery. I did the ammeter test the one day and pulled every MB fuse in the box and my own additions and nothing dropped the draw. It ended up on the alternator.

Something to keep in mind.

Battery drain 300sd
 

My 85 300sd had a battery drain. Looked at night and driver side back door "puddle" light was staying on. I removed bulb. No more problem.

In my ‘83 SD, the antenna motor occasionally got stuck retracting.

Sixto
98 E320s sedan and wagon

https://memegenerator.net/img/instan...hrough-you.jpg

-Rog

I don't know what you have against disconnecting the battery terminal? That will give you one answer to the question of the battery being either being good or bad. The second answer you need to know is whether or not the alternator is causing the battery drain due to a bad diode. With your positive battery battery lead disconnected from the positive alternator post, put your multi tester in the "continuity" mode, place one lead on the disconnected positive alternator post and the other lead against the alternator body. If you have continuity, reverse the leads of you multi tester. If you still have continuity, one or more of your diodes is bad. You should only have continuity in one direction.

Seriously, this thread is 8 years old.

-Rog