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Headlight Fades in and out

Discussion in 'The Garage' started by Port, Sep 14, 2020.

  1. Port

    Port XS650 Addict

    1981 XS650 SH

    I am having a headlight issue that i am trying to diagnose before throwing money at it.

    When riding, if i rev high then the light goes to shit.
    If i dog it a bit and run in at just around 3K RPM then i can get a little bit of light to throw down.
    If i pull in the clutch after about 2 seconds the light pops back bright.
    sitting at idle the light shines nicely

    Safety Relay(s) has been removed and bypassed (Red/white,Red/White, Red/Yellow twisted together)
    RLU was been removed and bypassed (Blue/Black, Blue/Green Twisted together)
    VR794 Reg/Rec conversion
    Ganzo Ignition Box
    Honda MP08 Coil
    Battery is at 12.58v after the ride

    Would a LED headlight possibly solve this as it would draw fewer watts? i was think of switching to one just for the higher light output.

    I suspect this problem may be a long standing gone, i rarely ride at night so quite surprised when i had a long ride home and hardly half a headlight.

    Weak rotor windings maybe?
  2. 5twins

    5twins XS650 Guru Top Contributor

    The problem may have to do with how you bypassed the safety relays. The 2 R/W wires are power into and out of the starter safety relay, on it's way to the starter solenoid. On your '81, there was also a second relay in that power path, from the switch on the clutch lever. This relay stopped starter function if you didn't pull the clutch lever in when the bike wasn't in neutral. So, you need to jump those R/W wires twice, 1st where they entered and exited the starter safety relay then again where they go into and out of the clutch switch relay. But neither of those would or should have any effect on your headlight operation.

    The R/Y wire is headlight power from the headlight fuse into the headlight auto-on safety relay. You shouldn't be bundling that with those R/W wires, it should be connected to the wire coming out of that headlight relay. I think this is where your issue is. The blue/black wire is the one coming out of that relay and running to the RLU. The RLU then sends that headlight power up to the hi/lo switch on the blue/green wire. Honestly, if you don't have the blue/black wire connected to anything, I'm not sure how your headlight is even getting any power at all now, lol.
  3. Port

    Port XS650 Addict

    To clarify what we're sayin, I made a couple of images. The top one shows how i have everything set up now and the bottom image is what i think you are suggesting that i change on where i am bypassing the safety relay.

    Also, is there a way to get the kill switch and Run Selector back working without the safety relays. I have looked around on the forum but couldnt find anything.

    As is:

    Suggested Change:
    Last edited: Sep 17, 2020
  4. 5twins

    5twins XS650 Guru Top Contributor

    The off/run/off switch is your kill switch. It's still working but not functioning correctly because you have, in effect, over ridden it by connecting the R/Y wire to the R/W's after the switch.You're feeding power into the R/W wires after the kill switch. Look at an '81 wiring diagram, it's all laid out there. Disconnect the R/Y from the R/W's and connect it to the blue/black. That will restore function to the kill switch and probably fix your headlight issues too.

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