Electrical problems - Mercedes-Benz Forum

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post #1 of 3 (permalink) Old 01-09-2009, 06:29 AM Thread Starter
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Electrical problems

Can anyone please help?
I have a 1997 E320 Merc which I am having trouble starting as something is draining the battery.
The RAA guy says that the battery and the alternator are both fine, but, something is draining the battery after a very short time.
Within 24 hours of charging, it takes 3 or 4 cranks before it starts and the next day, it wont start at all.
The battery cranks well.
Please help as my last hope is the Auto Electrics place and that will probably be expensive.

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post #2 of 3 (permalink) Old 01-11-2009, 01:28 PM
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Do you have any consumers plugged into the accessory sockets like a cell phone charger or anything?

Also get in the trunk to make sure the trunk light switch is making good contact while closed.

Sit in the car in a dark garage or at night to make sure NO interior door lights or any other lights are staying on.

Check your glove box light as well, but it should only work with key on.

If no results are evident you can do a draw test with an digital volt/ohm meter to check for a milliamp draw on the battery between the negative post and negative cable of the battery.

Connect the meter to neg terminal and negative post of battery and touch the cable to the post for one minute, then separate the negative cable from the battery and post while your meter leads are still connetcted to the post and cable end.

Your milliamp draw will be high if a consumer is sucking down the system.

Go to the fuse box and start pulling and replacing fuses one by one until your draw drops way down.
Once your draw drops, then something on (that) circuit from the fuse you removed will be the culprite.

Find out all that is powered by that fuse and check each item one by one.

Sometimes all it takes is unplugging a seat control module or a light switch, but it may take some removal of panels or seats.

Get your owners manual and find all the fuse box locations for your car.

Some advice.

You may want to take this car to a mercedes independent shop instead of the dealer or just a general repair shop to save some money on bogus charges, and unfamiliarity with the product but call first to make sure they have techs that are good at finding electrical draws.
Of course this is if you don't figure it out yourself.

Another thing to check is any aftermarket accessories installed in your car.
Unplug their power source and see if your problem goes away.

Last edited by benzfixer; 01-11-2009 at 01:30 PM.
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post #3 of 3 (permalink) Old 01-16-2009, 02:42 AM Thread Starter
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Thanks a lot Benzfixer...you are a genius!
I will be tackling that tomorrow.
Can I ask one more question...do you think that it is a good idea to get a 12 V battery charger and charge it up overnight?
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