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Thread: Electric. Nonsense.

  1. #1
    Junior Member Mortown's Avatar
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    Electric. Nonsense.

    Hi Guys,

    Firstly, this is my first post on here, I've been following it for a while and used some of the threads. I was planning on posting about a rough running carb however I now have BIGGER issues 😱.

    So, backstory is, a few month ago I purchased a 2000 TW125 (UK), the bike was ready to go and was a touch rough round the edges on 27k miles. I've ridden it a fair whack over the past few month but never in the rain/wet. Last week I braved the elements (very light rain) and took her out.

    Half way through the ride I noticed the indicators weren't working, headed home and upon stopping, the engine cut out (carb issue) however I had no electrics at all. My model is electric start only.

    So of course the main fuse had blown, my assumption was maybes some water in one of the connections. Stripped off seat/tank/headlight and got access to all wires. So, what I've done so far, opened every connection, sprayed with contact cleaner and blown with air, inspected all wires looking for any exposed wire, opened and cleaned handlebar switches. I can't find anything obviously wrong however as soon as I put another fuse it, it blows. That's even with the keys out and ignition off.

    I've spent the past 5 days trying various things I've seen on forums such as "shaking all the wires". I've checked and cleaned the 3 earth points I could find.

    Does anyone have any sort of idea as to what it could be ? Perhaps it happening during the rain was a coincidence ? I feel like the fact it's happening at all times is a clue however electrics baffle me so I have no idea.

    Oh, also, I've disconnected all plugs and connections and put the fuse in and the only 2 that it doesn't blow for are: regulator rectifier and starter relay. But that could be because I'm breaking the circuit myself ?

    Thanks all.

  2. #2
    Senior Member MtnMan75's Avatar
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    Do you have an ohmmeter? Troubleshooting by blowing fuses is not a very safe approach.

    That said, lets do this as a starting point assuming you have an ohmmeter:
    1. Remove the battery
    2. Set the ohmmeter to the lowest scale
    3. Unhook all connectors
    4. Put the key in the ignition and switch to on, make sure all other switches are in a neutral position(blinker), low beam or off.
    5. Put the ohmmeter between the BIKE SIDE (not the battery side) of the fuse holder and GROUND
    6. Attach each connector and note if the resistance falls below 2 ohms. On connectors that lead to switches, toggle the switches while watching the ohmmeter before moving on to the next connector. (The engine stop switch WILL show a ground - 0 ohms - when pressed) (note - Connect the CDI last in this process.)
    If you find a connector that drops your resistance below 2 ohms , your problem lies in associated wiring/components in that area beyond the last connector you attached - do step 2 listed below on only that connector.
    Keep in mind the headlamp switch circuit will look like a very low reading with the bulb installed especially when switched to high beam, and will ride a little above the 2.4 ohm reading depending on bulb. If your resistance is falling close to 0 on this even with the light installed, this wiring is still suspect.
    If not, do the following:
    1. Unhook all the connectors once again, remove the key from the ignition
    2. Check between each pin on every connector and ground (except wires that already lead to a ground point and these should be black)
    If this still doesn't produce a noticeable result, I'd start suspecting the CDI as the source of the problem.

    (Personal experience, things such as neutral switches, magneto wiring, kickstand switch, brake light switches... or anything else down low on the bike that catches more muck has a higher change of grounding out if the seals/sealant on those switches rot out and they are holding moisture). The magneto wiring and neutral switch wiring fall prey to heat over time and break down insulation.
    Last edited by MtnMan75; 08-03-2019 at 09:31 AM.
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  3. #3
    Junior Member Mortown's Avatar
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    Thanks MtnMan.

    It was a strange one. Eventually removed the Regulator rectifier, checked the resistance between the power input (Red wire) and the earth point on the RRs body and found it be to zero.

    I've ordered a new RR, chinese version from ebay so fingers crossed 🙈, that should arrive tomorrow and we'll see how it behaves then.
    MtnMan75 likes this.

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  5. #4
    Senior Member Fred's Avatar
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    The logic behind MtnMan75's approach to identify a short should be understood and practiced by all of us. Well done!
    2003 TW200 "Betty Boop"
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  6. #5
    Senior Member MtnMan75's Avatar
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    Hopefully that's got you back in business. Most likely it was just a bad R/R, but keep in mind that sometimes something beyond it (which is the whole bike, can draw on the regulator hard enough to heat it into it's death). If you still have things apart, you could ohmmeter like a crazed person on the connectors , if nothing else kind of helps you to know what feeds what when you're out on the road and something odd happens again. Let me know how things turn out.

    Thank you for the kind words, Fred.

  7. #6
    Senior Member MtnMan75's Avatar
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    Hey... clarify something for me... Were you looking toward the R/R on the red wire and ground, or with the R/R removed looking at the connector toward the bike from the red wire and ground? If you were looking toward the R/R you can almost be certain it was the R/R if you take a measurement between the red wire and the outside of the case. If that shows a short, that is definitely a problem. If you were looking towards the bike's wiring with the R/R unhooked, your problem isn't the R/R.
    Last edited by MtnMan75; 08-04-2019 at 11:10 AM.

  8. #7
    Senior Member TW_in_BC's Avatar
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    MtnMan75's method is precise and should resolve the problem.
    In the future, a method I've used (in building and automotive electrics) to locate shorts (ie: fault to ground, NOT intermittent) is by replacing the fuse with a light bulb.
    The bulb will act as a sink and prevent high current that would melt wiring, in other words it will light up...then you move along and check all points downstream of the bulb.
    When the bulb goes out...you've found the short....or at least, the section of wiring where the short is located.

    This may or may not work when dealing with electronic components (unless they are shorted internally), but it should put you in the ballpark.

    Keep an eye out for PO "repairs" that involve crimps and electrical tape...these are notorious for corroding and falling apart when they get wet. Also look for chafed wiring where the harness goes around the steering column.
    Last edited by TW_in_BC; 08-04-2019 at 11:36 AM.
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  9. #8
    Junior Member Mortown's Avatar
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    So I had taken the RR out, and tested the resistance between the bottom right pin and the body. The bottom right pin is where the red wire connects, I believe it's power for the transistor within the RR.

    For the bikes electrics, I followed your advice and checked from the circuit side of the fuse to ground and with the RR unplugged got infinite but with the RR plugged, got 0.002. It threw me at first as I assumed the short to be on the battery circuit rather than anything to do with the charging circuit but as soon as i clicked the RR had a source from the battery it made sense. I also did a diode test on the RR and got some very unusual results so I think the full thing is fried.
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  10. #9
    Senior Member MtnMan75's Avatar
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    Ok... yep that is definitely a problem. Should be an infinite resistance from that pin to the casing in forward polarity, in reverse polarity you would probably see something around 10M ohms (and what you are looking at doing this is the regulator portion of the R/R). If you ever wanted to check the rectifier section of the R/R (the diodes), you would take a reading one direction and then the other from the bottom right (red wire's pin) to each of the other three connections. One direction would show an infinite block to current, while the other side should show you something in the neighborhood of a .505 forward voltage drop. Let us know when your sprockets are turning again, buddy!

  11. #10
    Junior Member Mortown's Avatar
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    Ok so that done the trick ! Plugged in the new RR and she's back to life. Thanks for the help
    MtnMan75 and Hoot Gibson like this.

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