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Old 12-30-2018, 10:44 PM
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Join Date: Aug 2002
Posts: 56
How to access battery on ML350 totally dead, no lights, nothing, even on charger

Today my 2011 ML350 Bluetec presented me with quite a dilemma. Apparently a modest cold night (40's Fahrenheit) must've cracked a plate in the battery or something because it went from driving just fine one day, to the next use (at night, after sitting all day) completely dead, no lights whatsoever except for the dimmest glow from the "MPH" and "x1000" in center of dash dials accompanied by fast beeping sound from the dash, until over time even that faded away to nothing. No light, no sound, dead.

Put my 6A charger on it overnight (12 hours). Nothing. Hooked up another battery in parallel with jumper cables to the jump post. Nothing, no lights. Blackness. Hooked another car with a 240A alternator in parallel to jump post and could just pull voltage up to 12V measured between the jump post and ground, without a flicker of lights on the dead car, and when jumper disconnected, measured 5.4V there, after all night with charger and all that jump time. That's one bad battery.

Now the dilemma. The battery is under the front passenger seat in the ML350, accessible only if you run the power seat fully forward on its tracks, and also upward in the rear with the backrest forward. Without power, you cannot move the seat, and cannot access the battery. The factory book says to hook up a charger to get seat power, but as I said, even putting double digit amps into the jump circuit, I could not get any power to anything in the vehicle, not even a telltale light.

I tried removing the seat but that too requires moving the seat forward and back to access fasteners. What to do.

Long story short, I thought about turning the fore-and-aft seat motor by hand to advance the seat, which got me thinking a better way to turn a motor is with power, which sent me searching for my factory schematics and a spare battery.

Thank goodness I thought of that.

By just popping off the cover around the switch on the base of the seat with a plastic tool, the plugs into the seat switch can easily be reached. The lower one has all the motor connections needed...

Applying 12V positive and negative power from my spare battery to the "Brown with white stripe" and "Black with white stripe" female pins on the connector, I was able to move the fore and aft motor. If it goes the wrong way, just reverse the wires. In a moment, the seat was forward.

Then you do the same with the "White with black stripe" and "Green" wire connectors to move the backrest.

Then finally, you do the same with the "Blue with white stripe" and "Black with white stripe" wires to move the rear of the seat upward.

That gives sufficient access to lift out the battery.

Again the wire colors from the lower connector disconnected from passenger side seat switch and powered with leads from my spare battery:

BRN/WH Fore and Aft

WH/BLK Backrest

BLU/WH Rear seat bottom up/down

Attached Thumbnails
How to access battery on ML350 totally dead, no lights, nothing, even on charger-1_removethis.jpg   How to access battery on ML350 totally dead, no lights, nothing, even on charger-2_justunclips.jpg   How to access battery on ML350 totally dead, no lights, nothing, even on charger-3_connector.jpg   How to access battery on ML350 totally dead, no lights, nothing, even on charger-4_unplugged.jpg   How to access battery on ML350 totally dead, no lights, nothing, even on charger-5_seewires.jpg  

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Old 12-30-2018, 11:35 PM
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Join Date: Sep 2013
Location: Alhambra California
Posts: 2,803
Good information. Thanks.
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Old 12-31-2018, 10:07 AM
Hirnbeiss's Avatar
ich fahre, also bin ich
Join Date: Mar 2002
Location: South Florida
Posts: 1,664
Good info, thanks. It sounds like you got 7+ years out of the battery , which is more than good. Here, they last around 3 due to the heat. Maybe you want to replace this one preventively in 2024.

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