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Thread: Parasitic Battery Drain

  1. #1
    Join Date
    Apr 2015
    Location
    Tennessee
    Posts
    1,736
    My Cars
    1998 BMW 328i

    Parasitic Battery Drain

    So the past few months I've had a nagging electrical problem pop up. Ill come out stoked to drive my car and it randomly won't turn on. Checking the battery with a voltmeter, it seems that my battery will be entirely drained overnight. Ive done some research into this and determined the cause to be parasitic drain.

    Im finally getting around to troubleshooting this. I borrowed an electrical tester from work for help. You calibrate the amperage and type of fuse being tested. Then you touch the leads to the fuse and it tells you the current drain on the circuit.

    So i poked around in my fuse box and it looks like fuse #33 (a red 10Amp fuse) is drawing .5 Amp of current when the car is Off.

    The fuse panel cover indicates this controls the parking lights. Any ideas where to go from here?

    Sent from my VS987 using Tapatalk

  2. #2
    Join Date
    Jun 2010
    Location
    NY
    Posts
    9,079
    My Cars
    1997 328i
    That's a strange device, usually you would remove the fuse and then plug in those leads and it would driectly measure the current and for a parasitic drain that would be ok because it should be well within what the meter can handle (usually around 10A). But what your using is measuring the voltage drop across the fuse and then converting that into current.

    So look up the schematic in the Bentley manual and see what fuse 33 supplies. Usually it's older E36 that have the bad wiring in the trunk, but I would start there, remove the trim in the trunk and expose all the wire looms (left side mostly), and then what goes into the left side of the trunk lid.
    Attn. NEWBIES: Use the search feature, 98% has already been discussed.
    Click the search button, select "search single content type", select the "e36 sub forum" specifically, try the "search titles" then try the "search entire posts".

  3. #3
    Join Date
    Jan 2005
    Location
    Japan
    Posts
    54,654
    My Cars
    11/88 E32 750iL+98 E36M3
    fuse 33 based on 1998 ETM:
    LIGHT SWITCH DETAILS
    PARK/TAIL/UNDERHOOD LIGHTS
    INTERIOR LIGHTS
    GLOVE BOX LIGHT/CASSETTE BOX/ASHTRAY LIGHT/CHARGING SOCKET/CIGAR LIGHTER
    RADIO/HIFI/TOP HIFI
    CELLULAR TELEPHONE (PROVISIONS)
    ON–BOARD COMPUTER (BC V)

    snap on description of the amp hound:
    Description
    • Use on 6, 12 and 24 V Electrical Systems
    • No need to remove a fuse which reduces the amount of time to determine the current in the circuit
    • Finding parasitic drains can now be done without resetting the offending circuit
    • No more pull a fuse, check the meter, pull a fuse, check the meter-instead, check the complete fuse box quickly
    • Will not short a circuit while the fuse is removed
    • Touch the probes to the top of the fuse
    • Tests all of the most common automotive fuses types and amp ranges
    • Intelligent audible tones and digital displays
    • Active circuit unit beeps three times and displays amp value
    • Inactive circuit beeps continuously and displays (000)
    • Open or blown fuse will not beep and displays (- - -)

    here a demo how am amp hound works https://www.youtube.com/watch?v=CDDGlk_NvWQ
    Last edited by shogun; 01-07-2018 at 11:03 PM.
    Shogun tricks and tips for the E32 series are HERE!

  4. #4
    Join Date
    Apr 2015
    Location
    Tennessee
    Posts
    1,736
    My Cars
    1998 BMW 328i
    I found a wiring diagram for that fused circuit, but i left it at work. Looks like it runs directly to the headlight switch, and then from the switch to the light sockets.

    So i figure ill check the voltage at each socket to see which one is getting juice when it shouldn't. And Then also try disconnecting the switch to see if that resolves my drain issue.

    I checked the trunk wire harness and it seemed ok.

    Sent from my VS987 using Tapatalk

  5. #5
    Join Date
    Jan 2005
    Location
    Japan
    Posts
    54,654
    My Cars
    11/88 E32 750iL+98 E36M3
    check these first, often a problem
    UNDERHOOD LIGHTS
    INTERIOR LIGHTS
    GLOVE BOX LIGHT
    Shogun tricks and tips for the E32 series are HERE!

  6. #6
    Join Date
    Feb 2005
    Location
    Long Island, NY
    Posts
    6,479
    My Cars
    1995 M3 - 2007 X5
    Quote Originally Posted by shogun View Post
    check these first, often a problem
    UNDERHOOD LIGHTS
    INTERIOR LIGHTS
    GLOVE BOX LIGHT
    Don't forget the trunk light.

  7. #7
    Join Date
    Apr 2015
    Location
    Tennessee
    Posts
    1,736
    My Cars
    1998 BMW 328i
    Wanted to update this for everyone. My problem was indeed the trunk light. It was staying on all the time, even when the car was off and the domelight switch was set to off. Hard to diagnose, since you cant see it with the trunk closed and it turns on when the trunk is opened. I eventually figured it out because I removed my rear seats and ski pass for unrelated reasons.

    I just removed the bulb and problem is solved for now.

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