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Thread: Electrical gremlin question 1990 K 75 RT

  1. #1
    Nick Kennedy
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    Electrical gremlin question 1990 K 75 RT

    I confess I'm pretty much a total electric idiot.
    My 1990 K 75 RT has a 5 month old battery.
    If I leave it disconnected it will hold 12.8 volts for weeks.
    If I leave it connected it slowly dies in 3-5 days.
    How do I check for a MA drain with a VOM?
    Do I set the VOM to say 200 MA and connect the leads between the negative battery post and the cable?
    When I do it reads zero. Anything I do reads zero.
    What am I doing wrong?
    I was hoping to find a low level drain and pull fuses until it stopped and then go from there.
    Help!Thanks in advance!

  2. #2
    Registered User kioolt's Avatar
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    Some VOM's have a different jack that you plug into for ma. Are you using the correct jack?
    2004 R1150RT 186,800 miles , 1991 K100LT 128,700 miles, 1982 R100RT 106,900 miles
    Total 422,400 BMW miles
    AMA,BMWRA,BMWMOA
    The cheapest thing on a BMW is the nut that connects the handlebars to the seat.

  3. #3
    Nick Kennedy
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    I've got the instruction book for the VOM
    I think I've got it set up correctly

  4. #4
    MOA #24991 Pauls1150's Avatar
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    Your description of the VOM setup sounds OK, maybe set it to a lower range... but "...it dies in 3-5 days" infers a fairly observable current draw.

    It also matters - a lot - which jacks you connect to on the front of the VOM. Also verify that the leads themselves are not open (non-conductive, or high resistance); many banana plugs and lead tip connectors get loose and intermittent inside.

    AND: many VOM's have a fuse inside, specifically to protect the instrument from incorrect hookup or too much current.... check that!

    By the way, all of these instruments (analog and digital) have some internal resistance (plus the test leads themselves), so the observed current will Always be a little less than what it would be if there was no meter in line.

  5. #5
    Nick Kennedy
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    So should I be able to put the meter between the battery negative post and the associated cable and see current flow there? Or the positive side? or does it matter?

  6. #6
    MOA #24991 Pauls1150's Avatar
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    Yes, correct; and it doesn't matter whether you're on the negative or positive side.

    What will change is the direction that the VOM's needle swings - if it goes negative, just swap the meter around to reverse it. If it's a high draw, and the needle goes "negative", it may be hard enough to cause damage to the meter, so start with a higher range and step your way down.

  7. #7
    Registered User kioolt's Avatar
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    It doesn't matter if you do the negative side or the positive side. What we are trying to tell use is the connections AT THE METER do matter. You use different jacks at the meter for checking voltage and current. Make sure you are plugged into the correct jacks on the meter for measuring current. On my Fluke meter I would use the ma jack and common and then set the knob to Amps. If you did do as I have stated and turned you key on you probably blew the fuse in your meter since you would have turned the headlight on pulling much more then the 200 ma's that your meter was set for.
    2004 R1150RT 186,800 miles , 1991 K100LT 128,700 miles, 1982 R100RT 106,900 miles
    Total 422,400 BMW miles
    AMA,BMWRA,BMWMOA
    The cheapest thing on a BMW is the nut that connects the handlebars to the seat.

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