Making a thread to document my findings on a recent battery drain with my '83 300D

I found that my car has a battery drain after it left my wife stranded at work. Brought it home and charged the battery over night and it worked fine until a few days after (which was yesterday). I had the car apart replacing the steering box and when I went to start it the car would crank slowly and not fire. Darn, dead battery again. Charge the battery and the battery won't take a charge.

Now thinking back this has occurred a few times in the past where the car would drain the battery while off, recent past to be more specific but I thought my wife left something on or it was the battery going out.

So I just bought a brand new, $150 battery ( I recall these not costing more than $110 ). Car cranks up just fine and I start tracing out the electrical system.

Fuse by fuse I still see 12v across the negative terminal and terminal connector. Then I get to the glow plug relay and disconnect both connectors and the voltage reading goes to zero.


So I am now under the assumption the glow plug relay is to blame. Current work around is to unplug the relay when parked and plug back in when driving it. My wife drives all of 1 mile to work so she will be fine with it plugged in.

tomorrow on my lunch I am hitting up the junk yard since they have two diesels in their inventory and a GP relay is $6. Hopefully one of the two relays is still there so I can test this theory.

I haven't dug deep enough to find out if I can crack open the relay and find the fault / repair it.

stay tuned for more exciting finds!

I had one that failed on. It would hum loudly when it did so and run the battery down quickly. That was on my 83 brown 300D back when it was only about ten years old. Never had it in any other diesel though.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

So I swapped relays out and with it all unplugged I still saw a reading of 12.1 volts between the negative terminal and cable.

Pulled the obvious fuses first. #2 which is the clock, some interior lights, switch over valve (what is that?), warnings buzzer.

Immediately saw the reading go from 12.3v to zero. So I think I found the culprit. Something on that circuit is acting up. For now I pulled the fuse. Did a function check and lights, horn, blinkers, etc work.


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measuring current on these circuits will tell you more than measuring voltage at the fusebox. use an analog ammeter and you will be able to see the clock taking pulses of current on the always-on circuit. everything else should show no current flowing.

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'77 240D, 504H, OM617.952, etc.

I need to see if I can borrow such a meter. I wasn't able to get an amp reading because its probably too low for my meter to read.

You don't need a meter to look for a current draw. Get a small ~5 watt lamp, and connect it between the battery - post and the ground cable (so that all current the car tries to draw goes through the lamp).

If the lamp lights brightly you know something on the car is trying to draw at least the rating of the lamp. You can now remove fuses, etc until the lamp goes out... then you know you've found the draw.

This is a very safe way to test for shorts since if a short exists the only thing that will happen is the lamp illuminating fully.

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.