does this sound like a short circuit ?

Discussion in 'Motorbike Technical Discussion' started by jiggle, Sep 9, 2003.

  1. jiggle

    jiggle Guest

    The electrics on my bike have completley failed, no ignition, lights or
    anything. The battery is fine and so are the fuses. I have a haynes manual
    but I'm pretty much a novice at this sort of thing. It states the likely
    cause is a frayed wire but as far as I can tell all the wiring looks in good
    condition. Can anyone tell me how I should go about finding the fault ?

    Any info / help is much appreciated
    jiggle, Sep 9, 2003
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  2. jiggle

    jiggle Guest

    thanks for the quick reply, the haynes states there are only 2 fuses (its a
    vespa scooter so there's not much to it) and they are both fine.
    jiggle, Sep 9, 2003
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  3. jiggle

    bowman Guest

    Get a cheap meter or a 12v test light and start working away from the
    battery's positive terminal. Short circuits usually blow fuses or (worst
    case) melt down the wiring harness.
    bowman, Sep 10, 2003
  4. jiggle

    Macgyver Guest

    Won't be a short circuit as such, but an open circuit. Grab your
    multimeter and start working back through the wiring. Check all your
    ground connections.. they're a common point of failure.

    Macgyver, Sep 10, 2003
  5. voltage check from battery positive to negative, battery positive to frame,
    fusebox to frame.

    If OK, check resistance/continuity of both fuses.

    If OK, replace fuses and check for voltage at ignition switch.

    If you've got any relays in the system, they're also suspect.

    If you've got a complete failure of all electrics, it's likely
    that you've found it by this point. For a complete failure, my bet
    would be something very basic such as a battery lead.
    r_kleinschmidt, Sep 10, 2003
  6. The symptoms he describes are "completely failed, no ignition, no lights".

    I'd expect it to probably drive the lights OK even if it couldn't
    drive the starter. You could also check for this condition by
    jumping it from a car battery. If it starts, it's the battery.
    r_kleinschmidt, Sep 11, 2003
  7. jiggle

    bowman Guest

    A lot of digital multimeters can also fool you. They typically have a high
    input impedance and don't really load the circuit. This means you can be
    downstream of a severely corroded connector, and still see 12.5 to 12.8
    volts, but if there was any load, the voltage would drop off drastically.
    Sometimes a 1057 bulb with a couple of leads soldered on, or one of the
    cheap testers with a bulb is a better tool than a top end Fluke multimeter.
    bowman, Sep 11, 2003
  8. jiggle

    motownmoto Guest

    Jiggle ......

    Battery cables, and leads from battery to starter, etc, gotta be clean
    clean. And a little coating of dielectric for good measure, after clean
    Just a little "haze" on the cable connecting to Pos side of battery can
    make a no start/power situation.


    '95 750 Nighthawk (big red)
    '95 Helix (little red)
    '93 Ninja (up 'n runnin')
    motownmoto, Sep 11, 2003
  9. I know I'm not always going to be smart when I work on a bike.

    The best way to compensate for not always being smart is to be
    stupid but obsessively methodical. Works pretty well a lot of
    those times when that flash of insight fails you.

    Enjoy your bike.
    r_kleinschmidt, Sep 13, 2003
  10. I agree that your subconscious can solve problems that are
    nicely contained. Some problems don't lend themselves to this

    One of my favorites was an all night session troubleshooting a
    computer problem. At nine the next morning, we still hadn't
    found it, an angry mob was forming outside the computer room
    and my boss kept sticking his head in the door to say he didn't
    think he could hold them off much more.

    At this point, I asked again for the umpteenth time whether there
    was anything in the test setup that might possibly be different
    from the one where the problem occurred. The guy who had been there
    when the orginal problem occurred scratched his head and allowed
    as how there was one other difference but it couldn't possibly
    be signifcant or have caused this problem, and of course that turned
    out to be the cause we'd spent all night looking for.

    The lesson I got out of all of this was never to rule out things
    that "can't possibly" be the cause of a problem. See "Fate is
    the Hunter" (the movie).
    r_kleinschmidt, Sep 15, 2003
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