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Electrical short w/ MotoGadget munit - help

Discussion in 'XJ Technical Chat' started by Taylo105, Sep 27, 2019.

  1. Taylo105

    Taylo105 Active Member

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    https://www.xjbikes.com/forums/threads/xj650rj-seca-build.111444/

    This is the thread for my build of my 82 xj650rj seca. I have a custom wiring harness using a MotoGadget m-unit. wiring diagram below.

    I've had the bike working 100% electronically for over the last year.

    The other day, I was trying to start up the bike and while holding the starter button for around 5 seconds, suddenly it stopped cranking. Here is a list of my diagnosis afterwards. I'm looking for feedback on what could be the culprit to help me focus my efforts. All of my testing/diagnosis has been with the power-on, bike off.
    - headlight bulb appears to have blown (hooking the headlight directly up to the battery yields no light
    - starter solenoid appears to have died (a new one has been purchased to replace)
    - My starter appears to be bad. I can currently in the process of waiting for a rebuild kit and will go through it per the write-up on this site to ensure that everything is good. I suspect that it will need new brushes, as when I took it apart to inspect, the brushes looked very worn down.
    - when having the reg/rec & the brown and green AC Gen cables hooked up at the same time, there appears to be some short occurring which causes the MotoGadget m-unit, and my speedo gauge to very quickly flash on & off. (either due to a ground, or a positive charge issue. I'm not 100% sure which). When unplugging 1 of them, all lights work on the bike.


    Any recommendations on where to focus my diagnosis on? My thought was that either I fried the Reg/Rec, but I didn't think that it really "kicked in" unless the bike was on and running. Or did I mess up my AC Generator?


    [​IMG]
     
  2. XJ550H

    XJ550H Well-Known Member Premium Member

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    ohm out the brown and green wires those wires hook to the brushes for the alternator. if worn past limit you will be getting low voltage
    if ohmng fails spec remove cover for alt and inspect brushes and clean the copper rings with a hard art eraser untill shinny like a new penny

    you should test the charging system output at battery low volts typically means brushes. high out put typically means voltage regulator.

    ohming stator white wires will tell you if stator has failed

    specs will be found here
    The Ultimate Relay, Switch, Sensor, and Diodes Guide
     
  3. XJ550H

    XJ550H Well-Known Member Premium Member

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    Last edited: Sep 28, 2019
  4. Taylo105

    Taylo105 Active Member

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    Thanks

    I purchased a new multimeter this morning as my old harbor freight one was on its last leg.
    Green and brown wires are testing at around 50 ohms. So that’s a little higher than spec. Haha

    I took off the cover, and took an eraser to the copper and got a slightly higher number.

    the left circle you gave is not a join in the 2 wires. The constant power and key in power are spectated. The right circle you gave is to show that I have a key on power running to the tail light. (Wasn’t diagrammed the correct way)
     
  5. Taylo105

    Taylo105 Active Member

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    When I test resistance between the 2 copper rings, I actually get 4.4ohms (just at the top tolerance for spec) so this leads me to believe that my issue is with something from the rings, to the 2pin connector.

    after some additional cleaning, I can get the resistance down to 14ohms
     
    Last edited: Sep 28, 2019
  6. Taylo105

    Taylo105 Active Member

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    So after a bunch of extra cleaning, I can get the resistance between the green and brown pins down to around 5.5ohms. This is still higher than the testing tolerance. When I check the resistance of the 3 white wires, I get 0.5Ohms.

    So this should mean that my culprit is the alternator rotor.
     
  7. XJ550H

    XJ550H Well-Known Member Premium Member

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    did you look at the brushes the brown and green wire connect to . look like solid blocks of metal? if those are to short you get a charging issue . brushes will also have crud on them

    touch the ends of your meter probe together see if you get 0 or a higher number you would subtract that from your test results.. smaller ohm readings are hard to test with a digital meter
    brush.PNG should be between 11 and 17 mm
     
    Last edited: Sep 28, 2019
  8. Taylo105

    Taylo105 Active Member

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    I will take a second look at the brushes. I wiped them down to get anything on them off. Is there a spec for the length of the brushes?
     
  9. XJ550H

    XJ550H Well-Known Member Premium Member

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    17mm new 11 mm shortest you will find 1 brush wears faster than the other(the one on outside ring should wear quickest)
    there should be a wear limit line on the side
    wear line.PNG
     
  10. Taylo105

    Taylo105 Active Member

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    Thanks! My brushes are well sighing spec size. I can see the wear mark too. I’m at 15mm In mine. So I’ll polish those up and re-test
     
  11. Taylo105

    Taylo105 Active Member

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    So after booking it all back up, I checked the resistance. I have a relative mode to help get an accurate reading. (0 out with both prongs touching) and the lowest reading I could get is 5.2 ohms.

    so I’ve found a good deal on a whole alternator on eBay. I’ll check the readings of that when it comes in and see if I can swap out parts to get I to spec. If not, then I’ll go the brand new route.
     
  12. XJ550H

    XJ550H Well-Known Member Premium Member

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    next step is to test diodes in Voltage regulator. and do a live voltage test . for that hook meter to battery and bring rpms up to 3k voltage should be 14.8 volts
    if higher than VR is bad.


    m unit web site talks about over amps flashing all lights to dissapate amps but they spec volt readings
     
  13. Polock

    Polock Well-Known Member

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    so it sounds like you rode the bike for a year. then the other day in a matter of five seconds the headlight blew, the solenoid went bad and the starter brushes wore out. and maybe the r/r went bad. wow, that's some bad luck.
    i noticed you didn't question that m-unit at all
     
  14. Taylo105

    Taylo105 Active Member

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    When it rains it pours right!?

    we’ll see what happens when my shipment of parts get in.
    • New starter solenoid with built in fuse
    • Used alternator from eBay
    • New starter brushes
    • New reg/rec
     
  15. sybe

    sybe Active Member

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    swap your start out on the munit with the horn to make sure its working. everytime you hit start the horn should beep. also test the aux out. I had an munit go and everything looked functional except my aux output went.
     
  16. Taylo105

    Taylo105 Active Member

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    So I’ve tested the munit and that appears to be working correctly.

    After installing the new reg/rec and solenoid i noticed that I was still having electrical issues. Turns out that even though my battery tested at 12.8v and would power the munit on and allow LED lights to turn on, that it is bad. I verified this by directly hooking up my thought to be bad headlight to my battery with 0 light showing, and then to another 12v battery for my quad and let there be light.... so this points to my battery being bad as well or instead... however you look at it
     
    Last edited: Oct 5, 2019
  17. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Yes, just like that.
     
  18. Taylo105

    Taylo105 Active Member

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    New MotoBatt MB12U battery has been purchased. I’ll wait for that to come in before continuing with the diagnosis and install.

    Hopefully I’ll be back on the road by next weekend.
     
  19. Taylo105

    Taylo105 Active Member

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    OKay, so after a week of waiting for a new battery to come into the mail, I still am unable to start the bike. It appears that the starter itself is bad.

    To recap my current state of issues:
    - Everything powers on correctly from the bike with key-on power. (M-unit turns on, aftermarket gauge turns on, headlights, signals, etc)
    - New battery was installed
    - New Reg/Rec was installed
    - New solenoid was installed
    - Battery holds charge at approx 12.8 volts
    - When the starter button is pressed, the m-units lights for the starter circuit quickly illuminate, and then power shuts off to the bike and the m-unit restarts (as well as the gauge since it is controlled via the aux/key-on power from the m-unit)
    - When following the starter circuit troubleshooting (https://xjbikes.com/forums/threads/how-to-test-your-starter-circuit.7828/), when I preform a continuity test between the battery and the engine case, I get almost no resistance which points at the starter.

    Currently taking the starter off of the bike and inspecting.
     
  20. Polock

    Polock Well-Known Member

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    something's not right here, no resistance from bat- to engine case is a good thing.
     
    k-moe likes this.

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