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Thread: 1972 R75/5 Voltage to Ground Question

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    1972 R75/5 Voltage to Ground Question

    I'm a new member, so thanks in advance for replies.

    I have a 1972 R75/5 Toaster. Can anyone tell me whether 13+ volts between the battery ground strap and the frame is normal for this bike? I'd like to know whether I should be looking for a wiring short. I was getting 0.56mA as well - but this disappeared after pushing/pulling the ignition "key" a few times. I've taken each turn indicator bulb and the rear tail-light bulb out, one at a time, and still get 13+ volts on the multimeter. Thanks.

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    rabid reader dbrick's Avatar
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    Quote Originally Posted by NigelS View Post
    Can anyone tell me whether 13+ volts between the battery ground strap and the frame is normal for this bike?
    Haven't had an Airhead in decades, but I'll bite:

    Doesn't the battery negative pole connect via a ground wire directly to the back end of the transmission? The back end of the transmission is bolted to the engine, which is bolted to the frame, so the potential between the battery negative pole and the frame should therefore be 0, not 13+ volts.

    13+ volts sounds like the battery potential. I don't see how it can be seen between the battery ground strap and the frame. Are you perhaps measuring from the positive terminal of the battery, and not the negative one?
    David Brick
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    2007 R1200R

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    Unfunded content provider tommcgee's Avatar
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    Quote Originally Posted by dbrick View Post
    Are you perhaps measuring from the positive terminal of the battery, and not the negative one?
    Easy to do, even for a trained electronic tech, but since it isn't what I'd expect to get for a reading, I'd double check the battery terminals AND the meter leads for polarity.
    Salty Fog Rally 2007, 2009, 2011, 2012, AND LOOKING FORWARD TO 2014!

    -Tom (KA1TOX)

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    Thanks David & Tom.

    David - yes, the battery ground strap bolts onto the rear side of the transmission housing etc. So like you, 13+ volts between the negative side of the battery and the frame, raises my eyebrows. Although I've read some bikes (not Toasters) can show 8 volts?

    Yes, I'm measuring the voltage between the negative terminal of the battery and the frame and the multimeter polarity is OK.

    This bike has a history of eating batteries ($$). I now disconnect the ground strap when the bike is parked. But with zero amperage reading now - I wanted to make sure I'm not about to chase a ghost of an electrical short where none exists.

    Thanks, N.

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    jimmy armour
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    battery draw

    disconnect the neg cable ,then put a 12 volt test lamp between the neg terminal on the battery, and the neg cable or earth if the lamp lights you have battery draw,check behind the front cover or under the gas tank for wiring faults ,hope this assists Jimmy

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    #4869 DennisDarrow's Avatar
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    You undoubtedly have a short someplace in your system. Could be a microamperage or heavy duty. What you are seeing is the battery dumping a load into ground. Back long ago a sure fire test for a short in the vehicle was to barely touch the ground cable to the battery. If you got a spark of any kind it was a definate sign of a short. This is of couse done with all systems shut down and in the darkest situation possible.........Time for you to start running on ohmeter through the various systems to trace the leakage........Good luck......God bless........Dennis

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    Unfunded content provider tommcgee's Avatar
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    Quote Originally Posted by jimwjarmour View Post
    disconnect the neg cable ,then put a 12 volt test lamp between the neg terminal on the battery, and the neg cable or earth if the lamp lights you have battery draw,check behind the front cover or under the gas tank for wiring faults ,hope this assists Jimmy
    He has a multimeter, why would he use a test light?

    I'll go along with the rest of what you suggest and I'll even go along with he test light method if you have no meter. Visual checks will prolly be what finds the problem.
    Salty Fog Rally 2007, 2009, 2011, 2012, AND LOOKING FORWARD TO 2014!

    -Tom (KA1TOX)

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    It sounds like there is a voltage leak somewhere: that is if a multimeter connected between the ground strap and the frame is showing 13V potential. I would disconnect the positive lead from the battery and make sure the voltage potential for the ground goes to zero - as a check. If the voltage is zero between the ground strap and engine with the positive battery cable disconnected but shows 13V with the positive lead connected - then there is a voltage leak.

    If so, I would first disconnect the alternator diode board and see if the potential stays zero when reconnecting the positive lead. This approach of reconnecting the positive battery terminal after isolating a specific section of the electrical system is a reasonably safe and effective way to troubleshoot such problems. If yours has fuses, trying this with each fuse removed individually should also be done. Good luck!
    Stan

    AH# 13238

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    jimmy armour
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    voltage potential

    hi tommcgee,to give you an answer,while you can have 12 volts potential, on the meter it may not light a 12 volt bulb,

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    Thank you all for your suggestions. I'll post the outcome when I get it sorted.

    Regards, N.

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