92 SL300-24 Electrical drain

Discussion in 'Electronics' started by Indigo, Aug 7, 2016.

  1. Indigo

    Indigo New Member

    Messages:
    27
    Joined:
    Jul 7, 2009
    Car:
    129 Sl, 209 Clk, B180 and an old Sprinter van
    Just had new track control arms and finally looking forward to blasting round the country in my 92 SL having planned a few road trips then the car developed a new fault !
    When stored in my garage, with doors unlocked so not to activate the alarm, I previously had six weeks before I had to recharge the battery
    However it's now reduced to flat in 24 hours,
    I noticed that door lights were staying on, so removed fuse 10, but the foot well light stayed on, so removed bulbs
    I then removed the large relay unit in the relay box that has something to do with lighting
    The battery is still showing a 12.v drain
    In a darkened garage I loosened each fuse under the bonnet fuse box but none gave any indication of a spark
    I'm now at a loss what could be causing the drain
    Has any one got any suggestions ?
    Thanks in advance
     

    Attached Files:

  2. RichardF

    RichardF Active Member

    Messages:
    547
    Joined:
    Aug 24, 2013
    Car:
    Sl 320
    Connect your meter up to the battery, remove one fuse at a time until you can identify the problem. Don't forget the fuse box in the boot.

    Do you know how much current is draining?

    (assuming it's not just a duff battery)
     
    Last edited: Aug 7, 2016
  3. OP
    OP
    Indigo

    Indigo New Member

    Messages:
    27
    Joined:
    Jul 7, 2009
    Car:
    129 Sl, 209 Clk, B180 and an old Sprinter van
    Cannot see that I've got a drain through a fused item as I loosened all fuses in the dark and tried to get them to spark,

    The clue to me is that the door puddle lights and footwell lights are staying on

    When removing fuse ten, the puddle lights go out but footwell lights staying on, presume there's some sort of device that keeps them on for a few seconds after shutting the door, but without a schematic I'm stuck

    I've sent Tony a PM to see if he can shine some light
     
  4. RichardF

    RichardF Active Member

    Messages:
    547
    Joined:
    Aug 24, 2013
    Car:
    Sl 320
    Could be the alternator. Worth hooking a meter up anyway, see how much of a drain you have.
    Did you pull the fuses in the boot too?
     
  5. OP
    OP
    Indigo

    Indigo New Member

    Messages:
    27
    Joined:
    Jul 7, 2009
    Car:
    129 Sl, 209 Clk, B180 and an old Sprinter van
    Yes, I covered the boot fuses, but I believe they operate the roof only

    Yes, I had considered the alternator, be a shame if it's died as still charges at 13.8v
     
  6. RichardF

    RichardF Active Member

    Messages:
    547
    Joined:
    Aug 24, 2013
    Car:
    Sl 320
    The boot fuses also cover C/L, Windows, roll bar, alarm, antenna, boot light.

    Alternator diode packs can cause a drain, even though they charge ok. Some cars you can just change the pack. Not sure about MB. If the drain is unfused, it'd be my 1st port of call.

    Have you measured the drain?
     
  7. OP
    OP
    Indigo

    Indigo New Member

    Messages:
    27
    Joined:
    Jul 7, 2009
    Car:
    129 Sl, 209 Clk, B180 and an old Sprinter van
    Thanks Richard
    No I haven't measured the drain, but will do, I'm a bit short of time this week but I'll let you know how I get on
    Regards
     
  8. optimusprime

    optimusprime MB Enthusiast

    Messages:
    3,259
    Joined:
    Dec 29, 2013
    Location:
    Kidderminster Worcestershire UK
    Car:
    Mercedes W124 260E M103
    This is a fault you get when alternator regulator needs replacing... It can and will go flat over night with this problem
     
  9. OP
    OP
    Indigo

    Indigo New Member

    Messages:
    27
    Joined:
    Jul 7, 2009
    Car:
    129 Sl, 209 Clk, B180 and an old Sprinter van
    Alternator

    Thanks OP,
    ill measure the voltage leak with the alternator unplugged, and report back
     
  10. OP
    OP
    Indigo

    Indigo New Member

    Messages:
    27
    Joined:
    Jul 7, 2009
    Car:
    129 Sl, 209 Clk, B180 and an old Sprinter van
    Found the fault !
    Turned out it was the electric aerial
    The mast was not returning fully, and as long as it was not fully seated seems was drawing a voltage, I simply oiled the mast and hey presto
    Now standby draw is 0.05 amp, clock presumably , and after two weeks garaged car still starts on the button.

    Thanks for all your help
     
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