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Old 04-22-2003, 09:20 AM
Registered User
Join Date: Sep 2002
Location: NE
Posts: 133
Electrical drain...

Hey folks,

I have an '85 190e 2.3 that has been really quite good to me. I am the second owner with 187,000K. The car is basically a rock when driving and the binders are better than my wife's new jeep by far. the tunring radius is super... the list goes on, I am surely preaching to the choir. The problem is I don't drive the car a whole lot, maybe once a week (have 02 Suzuki GSF600S that I prefer to take) and when I go try to take it out the battery is typically just about dead. I have a trickle charger that I picked up for the bike byut only use on the car and I set it up for a couple of minutes and the car is ready to go. The car never stalls once started, never. So point is I have this car that runs like a top but the battery is being drained somehow and I would like to trouble shoot it. Here is my question: could anyone give me recommendations for books to read on troubleshooting automotive electrical systems? I COULD say that the battery is new, and the ground next to the battery on the suspension is rust free. I was able to take out the voltage regulator without removing the alternator and there is about an inch to an inch and a half remaining which is in specs... but the truth is I doubt anyone will be able to come up with an answer for me without my first getting a better handle on it myself. So, that's it, you know the car I have and what sort of reading I am looking for, thanks in advance for your help.


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Old 04-22-2003, 11:41 AM
Super Moderator
Join Date: Apr 2000
Location: Falls Church, VA
Posts: 5,316
You need to get a digital multimeter and test your battery and charging system. If they are OK, then you need to look for a drain when the car is off.

Try a search - there are lots of posts on this problem and how to isolate it.
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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Old 04-22-2003, 11:48 AM
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Join Date: Jun 2000
Location: SF Bay Area
Posts: 20,800
Check the current draw with the engine off, key out. Pull the fuses out until you find the circuit with the greatest draw. Go from there.

Check how much DC amperage your multimeter will handle.

91 300SE
87 300SDL
83 300SD
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Old 04-22-2003, 11:49 AM
I told you so!
Join Date: Jun 2002
Location: Motor City, MI
Posts: 2,844
Checking for Battery Drain

A good way to check for battery drain is to remove a battery cable, set it near the post, and complete the circuit between the cable and post with a 12v light, LED, or multimeter. If the light is lighting or you're drawing more than 30 milliamps, you have a drain on the battery and can then proceed to remove the fuses one by one. When the light goes out, the circuit that is serviced by that fuse is draining your battery and you can concentrate your search there.

It could be something like a glove box light or trunk light that stays on.
95 E320 Cabriolet, 153K
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Old 04-23-2003, 10:56 PM
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Join Date: Nov 1999
Location: Venice, FL - "sharktooth capital of the world"
Posts: 712

That's a great idea! How come I never thought of that!

I will for now on. Thanks,
85 300D 310K (sold)
90 350SDL 184K sold
83 300D 118K (sold)
88 300E 153k (sold)
93 400E 105K (sold)
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Old 04-24-2003, 12:20 AM
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Join Date: Dec 2001
Posts: 573
Hooking up a test light as suggested or using the amp scale on a voltage-ohm-meter(VOM) may be of help, but don't be surprised if after pulling all fuses from under the hood that the light stays on or the milliamp reading on the VOM stays higher than avg.

If this happens, consider "aftermarket" accessories.

I've long suspected that some alarm systems love electrons.
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Old 04-24-2003, 01:22 PM
John F
Posts: n/a
Check your negative cable. Awhile back, I had a '71 Westphalia VW bus. Similar situation, as you descibe. Turns out the negative cable was corroded. You couldn't see it but it was enough to drain the battery. Once I replaced it, I cut the old one in two. It was as green as "crest" toothpaste!!
Good luck, John F.
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Old 04-24-2003, 02:15 PM
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Join Date: Sep 2002
Location: NE
Posts: 133

thanks guys but don't bother posting unless you really want to, with your collective help I fixed the problem... see newest post on transmission fluid if you are interested in details.

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Old 04-25-2003, 07:41 PM
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Join Date: Sep 2002
Location: Kingsport, TN
Posts: 375
Hi tunk,

I used Haynes Automotive Electrical Manual. First from the library, then I bought it.

Gives a good start for somebody who does not know much about car electrics.

Reinhard Kreutzer
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Old 04-25-2003, 10:20 PM
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Join Date: Mar 2003
Location: Southern California
Posts: 2,161
Even inexpensive multimeters have an ammeter function that will measure small currents. Just disconnect the negative battery cable with someone holding the test leads to maintain continuity or use test leads with alligator clips. (You hook the meter in series to measure current.)

The nominal current draw is about 30-40 milliamps and it pulses due to the clock.


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