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  #1  
Old 05-26-2012, 07:44 PM
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1991 190E 2.6 - battery drain

Hello all. Sorry, another battery drain issue. I've already gone through the forum and net searching for similar issue and found some really good one but none helped my cause.

My battery is 9mos old. Battery ran out of juice 3 days ago. I was able to jump start it and following day, it died again. When I say died, not enough power to light interior or cluster lights.

I had autozone checked the battery and they found it ok. It charged for about 30 minutes and it did not discharged. They also checked my alternator and found to be operating normally.

When I got home, I disconnected the negative cable and left it over night. Following day, I connected the cable and was able to start the car. So, it held its charge while not connected overnight.

I connected an analog ammeter between the battery negative post and ground cable. I set the meter to 500ma and check drain, it would peg the meter. So I set the meter to 50V and now it display a safe 75mA without pegging the meter. So let's start with that, 75mA more or less.

What I did so far:
I removed all fuse and relays and connectors I could find under the hood and the drain did not drop. When I say "all", I literally mean it. I removed all fuse from the fuse box at once, drain didn't drop. I removed all relays; OVP, and other relays that are under cover, drain didn't drop.

I removed cables from alternator, drain didn't drop.

I removed power from antenna, radio, power vacuum(under the rear seat), power from the component under the mat(passenger side), drain didn't drop.

I removed every connector that looks like can be disconnected, drain didn't drop.

What is it!

Help?

Last edited by javelin; 05-26-2012 at 08:09 PM.
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Old 05-26-2012, 08:04 PM
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disconnect the alternator. good luck, chuck.
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Old 05-26-2012, 08:08 PM
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Quote:
Originally Posted by porkface View Post
disconnect the alternator. good luck, chuck.
Thanks I did that already. Drain didn't drop. I edited my original post and changed "starter" to "alternator". I still have to check the starter.
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Old 05-27-2012, 09:26 AM
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Re: Battery drain

I believe that model has a two or 3 piece radio system. On the passenger side trunk behind the liner is some of the radio system. It is a tuner and /or two amplifier system. Hold your hand on these components to see which one might still be warm after your car sets. If warm, you have found the drain. You can also unplug the power wire or on in unit fuses to see what happens. Sometimes the power to the antenna sticks on so you must unplug the power from the unit on the power antenna. The amplifier box stuck on on mine which was a 124 model. You should also use a digital voltmeter to look for the drain by testing the battery voltage after you have disconnected something and waited a while because digital is more sensitive. Chances are its a rear trunk ampliflier.
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Old 05-27-2012, 03:54 PM
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Quote:
Originally Posted by ohiomike View Post
I believe that model has a two or 3 piece radio system. On the passenger side trunk behind the liner is some of the radio system. It is a tuner and /or two amplifier system. Hold your hand on these components to see which one might still be warm after your car sets. If warm, you have found the drain. You can also unplug the power wire or on in unit fuses to see what happens. Sometimes the power to the antenna sticks on so you must unplug the power from the unit on the power antenna. The amplifier box stuck on on mine which was a 124 model. You should also use a digital voltmeter to look for the drain by testing the battery voltage after you have disconnected something and waited a while because digital is more sensitive. Chances are its a rear trunk ampliflier.
Thanks Mike. I was able to locate only one amplifier in the trunk, passenger side, located behind the plastic cover/lining and is bolted down near the gas cap on the upper right side. It was cold to the touch. I even removed the cables connector, measured drain, but no drop.

What component or device would drain at a constant rate of 75mA?
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Old 05-27-2012, 05:24 PM
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Battery Drain

I think what you found was a tuner box. The in-dash unit is just a remote for that tuner in the trunk. If it's like my 1991 126 model...the amps are behind the back of the back seat back. You have to take the seat bottom out, then there are 3 screws to take out the back. One screw on each bottom side and one screw in the bottom middle. But, I am thinking if you take the fuse out of the tuner then the amps will be go unpowered. I just dont know.

Other than that you can disconnect the antenna power in the trunk on the drivers side in case that sticks on. Other than that I just dont know. In my case I had a digital meter and did what you did and everything checked out even the battery. So an MB mechanic gave me a hint that it might be that screwy setup on the radio system....he was right. That was a 400E and the amps were separate (2 of them) behind the trunk panel along with the tuner. Did you take out the fuses that dont go thru the fuse block...one of them is the trunk tuner and I think the radio head in the dash is fused, too. It took me a month of checking things out before I spoke to a mechanic friend and found that bad amp.

Until you find out what is causing the drain you can just unhook the battery like I did and rehook it when you want to drive it.
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Old 05-27-2012, 08:20 PM
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Thanks Mike. I removed the back seat like you said and found no amp there. I think the 190E has one amp and it's the one I found in the trunk. It has the cooling fins.

I truly appreciate your suggestions. Kept me looking...

There is one last item I never checked yet and that is the starter. It's just because I don't want to go under the car just yet.
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Old 05-27-2012, 11:42 PM
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Battery Drain

I am curious. Let me now what you find.
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Old 05-28-2012, 03:23 PM
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75ma is a negligable amount of current. That's .075 amps. At that rate, a 60 amp hour battery would last 800 hours. So, perhaps you are not reading the meter correctly. If you are reading correctly, than that current would be acceptable, as some keep alive current is required by various electronic components, like the radio, alarm system, remote door locks, clock, and engine control computers. Get a real amp meter capable of reading up to 5 amps directly. For a good battery to go down quickly, the current draw will be very high. Most likely cause of a bad battery, even a near new one, is a bad battery. Internal resistance is to blame.
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