Hey gang,

Got an electrical question for you. I recently replaced my battery due to my car regularly not starting and a very old battery. Upon receiving the new one, I continued to have the dead battery in the morning. I hooked up the charger and charged it to full and removed. The next morning the battery was down to 3V. I then proceeded to do the parasitic test and removed the positive cable and stuck an ammeter in-line. I'm reading 1 mili-amp or 0.01a which I deemed to be well below the acceptable allowance. Now I'm stumped. How is my battery draining if there isn't a load on the battery when the key is off? Mind you, this has all been with ignition off, my alternator checked good and the battery will drain a full charge without ever even starting the car. Any help appreciated as always.

184 300d turbo 147k
check for glow plug relay at glow plugs maybe staying on 12 volts on 5 plugs, left side of engine, pull one fuse at time, radio
ant on, light glove box, trunk light on , unplug alternator, diode,
starter relay 3 wires at pass side near battery

Thanks for the reply, I will check there. However, wouldn't I see this on my ammeter check on the battery if the plugs were drawing?

I thought I found it a little bit ago, when I realized the trunk light wires had been cut by the previous owner and left bare and stuffed in the trunk lid. I blew the fuse pulling them out. Got all excited until a couple hours later when I checked battery voltage and it is still draining slowly. Still waiting to see if levels off.

0.01 amp is 10 milliamps. Even that isn't enough to drain a battery in the short time you describe, I just want you to be sure of your units.

Here's a simple test. With the battery charged and reading 12.5 volts or more on your voltmeter, and with the negative cable disconnected from the battery, carefully and gently tap the negative cable on the negative post of the battery. The point here is to try to get a spark when the connection is made. No current, no spark. Little spark = little current. Bigger spark = more current. The bigger the spark, the faster the battery will drain. Do this test and report back.

Jeremy

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Jeremy,
Agreed. 10 milliamps. I've read acceptable is up to 35 milliamps. No spark on the neg cable tap.

I didn't think garden variety multimeters measured DC current. Are you sure you are measuring DC current? My multimeter didn't so I had to use a one ohm resistor to measure the current draw.

__________________
Kevin

1978 300D
1979 240D

Assuming one was using garden variety and not Fluke

Didn't know you had the 'good' kind.

__________________
Kevin

1978 300D
1979 240D

I have this exact same problem with my '78 300D
It will drain a yellow top optima in 2 days.
I'm getting about a 30 milliamp draw.
I get a pretty decent spark when I do the negative cable test.
Where exactly is the glowplug realty and how do I check it?
Any help would be appreciated.
Thanks.

I believe the relay is under the dash, but hopefully more knowledgeable forum members will chime in. I would pull it for a couple of days and see if this solves the problem. Do you have an electric antennae? I think this has been a problem for others in the past. This thread might help. where is the glow plug relay on my 300D (1978)?

__________________
Kevin

1978 300D
1979 240D

If your Glow Plug Relay is not on the driverside fender well (trace the wires from the Glow Plugs back) it is most likely behind the instrument cluster; a silver metal relay box. (In this part of the Forum I have not read a good way to troubleshoot the behind the instrument cluster Glow Plug Relay.)
You might want to hunt through this site for info:
http://www.pauldrayton.com/uploadfiles/merc/Service/W123/Index/616index.html

__________________
84 300D, 82 Volvo 244Gl Diesel

Thanks for the replies guys.
The power antenna was removed by the PO, so that can't be the problem.
I'll look for that relay this weekend.

Found the wires to my trunk light had been cut and stuffed bare wire into the trunk cavity with no caps. Not sure how it didn't blow a fuse when it touched the metal as it did when I was pulling them out. Spliced the wires back together (trunk light still doesn't work), and battery seems to be holding charge. A few hours time will tell.