[W126 Coupe] BATTERY DRAIN

[Iain Gunn]

Battery drains are tricky things to find. Usually you go back to the last thing worked on or installed. Did you have a new accessory installed?
Some known things to cause drains are the power door lock pump. If there is a leak in to system it will run intermittently. Also the power antenna.
Here's a thing my dad taught me. In dim light or darkness, pull the negative off the battery and just touch it back on the terminal, if you see a large spark, something is draining. Remember there are a few things that are always powered, so if you barely see a spark, could be one of those things. Then go and start pulling fuses and repeat until you find the circuit. That at least gets you in the right direction.
Before you do all this though, check the items that Vance posted. Once you have answered # 3 disconnect the ground on the battery and leave the same amount of time. Hook back up and see if the engine turns over.
See below on Vance's items
  ----- Original Message ----- 
  From: Vance Rowley 
  To: Mercedes Coupes Mailing Lists 
  Sent: Saturday, June 20, 2009 7:48 AM
  Subject: Re: [W126 Coupe] BATTERY DRAIN


  Most of the things that a professional mechanic or auto electrician would check for a battery drain (at least at first) can be checked by yourself as long as you have a very basic knowledge of electricity and a multi-meter.
  No codes would tell you or locate a battery drain. A few more details are required to help you locate the problem.

  1. Are you sure that your battery itself is OK? HAVE A LOAD TEST DONE ON IT.
  2. How long does it take to drain the battery enough not to start the next time with the car just sitting? 
      (Several hours, overnight, two or three days?)  SEE MY ANSWER ABOVE.
  3. What is the battery voltage with ignition off while at rest? SHOULD BE 12 V
  4. What is the battery voltage with the engine running? SHOULD BE AROUND 14 V
  5. How much of a current draw are you getting from the battery with ignition off?

  If you could answer at least some of the questions and provide a few more details of the symptoms and what you have checked so far, I am confident that this group can help you to some degree, and might even be able to offer a solution.

  Regards,

  Vance.
    ----- Original Message ----- 
    From: clay 
    To: MBCOUPES at MBCOUPES.COM 
    Sent: Friday, June 19, 2009 8:59 PM
    Subject: [W126 Coupe] BATTERY DRAIN


    Hi Guys,
    Out of hospital again, it's getting to be like going to get the SEC fixed. Broke ankle on both sides and couldn't get surgery do to the block cloth that made me fall. Enough of that, I and my son still can't find drain but when I went to start the last few times the wipers come on for a couple of sweeps, Could the drain be in ignition switch or the stalk or horns or column ? The shop I used to tune the 450SLC for emissions test charges $89.00 per hour. I guess I'm wondering how long a Mercedes shop w/trained mechanics would take to locate drain (ball park). Is there a plug in for codes on a 1988 SEC ? Any info highly appreciated especially Dick, He's helped me alot.
    Thanks Alot,
    Clayton Moizo
    Scottsdale,AZ
    If anyone wants to call in in bed again for at least another month or 2.
    Home 480.368.1217
    Cell 480.268.0791


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