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Bad ground or short circuit?

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by zukboy, May 7, 2014.

  1. Hi All

    without copping too much hate this is a post about an electrical issue with a scooter.

    recently purchased a PGO Arriba dirt cheap for city run arounds however it has one slight issue - the electricals are messed up. I have purchased a new battery and checked the rectifier/regulator ( works fine) and the charging system is working A ok. there are a few strange symptoms :

    * the starter motor does not work unless the engine is already running.
    * the indicators do not flash however when the engine accelerates, the relay switch squeals and the indicator display flashes very quickly.
    * previously when brakes were applied the headlights would come on, and if headlights were already on, applying the brakes would switch them off.
    * horn works poorly unless engine is revving --> then works fine.

    i'm don't have much experience with electrical but it sounds that there is either a cross connection, bad ground or short circuit somewhere.

    anyone have any pointers on how to diagnose the issue ?

    I was also able to track down the wiring diagram ( attached)

    Attached Files:

  2. Bad ground You haven't got all the wiring diagram though, it doesn't show the indicator circuit, ignition circuit etc.

    The first step would be to check all the electrical connection plugs for clean connections and no melting or deformation of the plug.
  3. thanks for that, I've found the full wiring diagram (attached)

    Attached Files:

  4. It sounds like a combination of issues.
    As CJ said above, make sure that all the connections look good and feel solid. Especially that the battery is properly connected to the chassis.
    I've seen similar problems when multiple circuits have not been earthed properly and the voltages try to find earth through other channels.

    If you have a continuity tester or multimeter check that all circuits do have a proper ground connection and that there's not a break anywhere hidden inside the insulation.
  5. Yep a major ground isn't connected to chasis. check for one near the battery floating loose or from the battery to chasis not connected
  6. If you are going to check the grounds, clean both surfaces with fine wet & dry & use a little dielectric grease to prevent any corrosion. Prevents moisture causing problems in the future.
  7. Wowsers, that's a lot of faults...

    Sounds like bad ground(s), bad battery/reg/rectifier, possibly +12V going somewhere it shouldn't &... maybe a lot corrosion.

    Has it been swimming in the bay ever?
    • Like Like x 1
  8. sounds like an entertaining ride.

    I've be checking the main earth cable to the negative on the battery. Check both ends are clean and have a good connection.

    Also, have you tried a different battery? It could be a physical electrode fault in the battery itself.

    once you are confident with those things, you need to work through the harness systematically.
  9. You might have found out why it was dirt cheap... :wacky:

    I'll have to see if I can nut-out a couple of likely contenders once the mother-in-law goes home. If you just try fixing evertyhing you'll be there for weeks. Although it might be a good idea to fix everything anyway...
  10. thanks all

    checked the main ground for the battery. cleaned the chassis contact point looks solid. tick.

    the battery is brand new and the regulator works fine. in any event the regulator would not be messing the DC system.

    the bizarre thing is that all components, particularly the starter motor) work when the engine is running but don't function on the only DC circuit. it could be that some renegade, previous owner tried to DIY wiring and messed it all. but the connectors all look like original components and seem relatively untouched.

    the exploring continues. does anyone have a systematic process on where to start. i presume a live voltage drop test for each component that draws major current.. horn, starter motor etc would be a start ? or should i go straight under the instrumental cluster and do indicators which are clearly not working
  11. OK so the battery is properly connected to the bike frame.
    Next I'd be checking the earth connection to each of the major components / switch groups.
    Make sure that each component has a direct link to ground ( where needed ).

    My next check would be the ignition switch to ensure that each pole are getting power correctly from the ignition, and that there's no short in the switch housing.
  12. There are some standard techniques, Pick a circuit and concentrate on fault finding that one first. Lets say the Horn, the Horn switch is a switched negative from the drawing you supplied so it is connected to positive when ignition is on and the horn button puts the negative on the other side when you press it.
    1. Attach the negative of your multimeter to the battery negative post.
    2. Ignition to ON
    3. Put the Multimeter positive on terminal 78 of the Horn, Green wire with Yellow tracer.
    4. It should be 12V or there abouts.
    5. Press the Horn button
    6. The voltage should drop to zero.
    If it does then check the other side of the horn to make sure you still have 12 v (while pressing the Horn button) if you don't the fault is upstream towards the positive of the battery.

    If it doesn't then the fault is downstream towards the negative of the battery and you will need to work your way down that part of the circuit, Horn Button and eventually to the battery negative.

    That's basically it, a poor connection should develop a voltage across it when you draw current and will rise or drop to the 12v or zero depending on which side of the battery it connects to when you are not drawing current.

    I hope that makes sense. :)
    • Like Like x 1
  13. Worth checking fuses are in good order.
    Had a multitude of issues on a Madass 125 that had a half melted fuse.
    Actually the fuse was okay, but one of the connecting pins melted through.
    It was correct rated fuse too...
  14. Hey Zukboy, any update on the issues you had ?
    Did you find a cause ?