Newbie, electrical drain 300te - Mercedes-Benz Forum

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post #1 of 3 (permalink) Old 09-28-2009, 03:56 PM Thread Starter
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Newbie, electrical drain 300te

New to me car, 1991 mercedes 300te

I have the car 20min starts, drives, no problems. Park it.... 8 hrs later D E A D. I jump it, and it fights, but starts up. drive it one hour home, runs fine, just before i turn her off I try the electronic seat adjustment and the headlights dim off and the radio goes out as i touch the switch. i try the window button, i pull up on it as the window is already up, the lights go off again, interior stuff as well. So it seems the alternator right?

i park over night, today it is dead again, so i replace the battery with a new one. put the positive terminal to the battery, and the negative to a test light then to the battery, it glows like a becon. i pull all fuses one at a time and the test light does not go out.

so what could it be?

i get 12.6 volts with the key in my hand. once started i get 13.5v so it seems the alternator is good. there is also an aftermarket kenwood installed, mabey it could have sucked the old battery dead.

If this thread is already posted again and again, i just need to be pointed in the right direction.

please help me
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post #2 of 3 (permalink) Old 09-28-2009, 04:47 PM
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I had the same problem with my 89 300E, and my mother's 88 260E. Both times it was the alternator. The alternator would test OK off the car, and upon initially starting it, it would test OK with a volt meter (13.5V+). However, if I let the car idle with the volt meter on it and the hood open, after the car would get up to temperature, the volt meter would dive to 0 and the car would stall. The battery light would never come on, and the parts store insisted nothing was wrong with the alternator. The problem went away after changing the alternator after chasing the problem for weeks. Same problem, both cars.

No guarantee that's your problem....but that's what I've encountered in my experience. You might just want to check that there's no lights staying on after the car is off (a dome light, trunk light, light in the bottom of the door), or make sure you don't have a bad corrosion on the ground cable from the battery to the chassis.

Hope this is of some use to you.....Good luck!

07 C280 4MATIC 80k Miles
00 E430 4MATIC 74k Miles
88 260E 201k Miles
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post #3 of 3 (permalink) Old 09-29-2009, 05:59 AM Thread Starter
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Last night i pulled all the fuses again, the test light was still on. i pulled the wire that went to the alternator as well. the light stayed on. i checked each wire that goes to the positive terminal, and i found the one wire that was lighting up. i am not sure what it is. i tried one more test, i left this wire off and tried to start her, the engine would crank and crank but not catch. with the wire on it started right up. i figure it has somthing to do with the brain mabey.

so again i disconnected that wire and put the test light on the battery lead and began to put all the fuses back and TTADA. i found that fuse "C" was the drain. it lists the power door locks, and has some connection to the drivers door, wich was broken when i got the car. the dapo that sold me the car told me you have to lock the car from the passenger door because the key will not turn in the drivers door.

today i will try to pull the door panel off, without breaking anything, and have a look.
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