'92 R100GS Electrical Dilemma

Discussion in 'Airheads' started by rob, Apr 18, 2021.

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  1. rob

    rob Been here awhile Supporter

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    On a recent weekend ride, I was told my brake light wasn't working. That was half right. My front brake light wasn't. A little while later, I noticed that I didn't have a high beam on my headlight. I've replaced it with a LED but still no high beam. Is there any connection between the headlight and brake light? I'm always afraid of letting out the magic smoke.

    Thanks for any help.

    Rob Lessen
    Arma, KS
    #1
  2. bmwrench

    bmwrench Long timer Supporter

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    There's no connection between the two. The original front brake switches on these bikes were so troublesome that a recall was done.
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  3. Warin

    Warin Retired

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    That font brake light switch is used frequently and sits out in the weather. High probability that is the problem for the stop light not illuminating. The switch wiring should lead down from the switch to a 2 pronged connector - separate it and then short the 2 connectors on the bike side (not the switch side) and see if the light come on. NOTE: these connections are at battery voltage and should not touch anything else... don't loose the smoke.

    The hi beam flash not working could also be the switch ... how clean is it?
    #3
  4. Beemeup

    Beemeup 1978 R100/7

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    And always check the other half of the equation, the grounds.
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  5. groop

    groop So much to ponder

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    For the brake switch, that's an easy check for continuity at the plug under the tank. Use your DMM and check for tone. If it's bad, replacements are easily available. For the headlight, it might be the bulb, the rocker switch on the left handlebar, or something else. If you have the original bulb, you can swap bulbs back and check. While the 'good' bulb is in there, check the rocker. There is a hidden ground that comes down from the headlight bucket and attaches behind the voltage regulator on the top of the frame
    #5
  6. Warin

    Warin Retired

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    As the stop light works with the rear brake ... it is not 'the grounds'.

    As the hi beam is only not working with the switch 'flash' function it is neither 'the grounds' nor the bulb... (assumed to work with the noral hi/low possitions)
    #6
  7. Beemeup

    Beemeup 1978 R100/7

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    That's a weird response. Always check the grounds when looking at connections, and make sure they are clean. The grounds go to each bulb so it makes no sense to just dismiss them for some odd reason.
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  8. Warin

    Warin Retired

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    The front stop light switch is not working... it has no 'grounds' of any description. In that circuit the 'ground' is on the rear stop light bulb. That is known to work as the rear stop light switch works by lighting up the rear stop light bulb.. thus the rear stop light ground MUST be working.

    Similar logic for the headlight.

    I have worked in electronics for a few decades on all kinds of systems (design, construct, maintain, modify, repair ... all of it). Electrics on airheads is child's play for me. How many years of knowledge do you have in this field?
    #8
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  9. Beemeup

    Beemeup 1978 R100/7

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    I was trained as an electrician in 1972 for Uncle Sam but I don't get the petty nature of your posts, please try to impress someone else and pound your chest elsewhere.

    What I said was a generic comment about always checking the grounds when troubleshooting anything, the return of the circuit. There is no front brake light so he could have just meant no brake light.

    Get over yourself.
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  10. Warin

    Warin Retired

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    My comments are not 'generic' but targeted at the problem thus avoiding pointless work.

    From the original post ...

    From this I assume that;

    • the front brake operation does not activate the rear brake light.
    • the rear brake operation does activate the rear brake light.


    Do you agree???

    Following that;

    The only ground in this circuit is at the rear brake light, as the rear brake light does operate the ground in this circuit is fine.

    My training started in '69. As an electrician, fitter and machinist and in electronics, yes all 3 together in trade schools, when not at school I was stationed at various depots working on both small and large equipment.
    #10
  11. Beemeup

    Beemeup 1978 R100/7

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    I didn't assume anything. He didn't say the rear switch operated the lamp, that's an assumption but the question was more on the possible relationship between that and the headlight, which is why I answered the way I did. This isn't a dick slinging contest, I was just pointing out something that many people miss in troubleshooting.
    #11
  12. rob

    rob Been here awhile Supporter

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    Do to family and work stuff, I finally got a chance to dig with y'll's help. I had to soak the front brake switch with Kroil for a few days be for I could loosen it. The switch plunger is stuck and soaking it with the Kroil for a couple of nights hasn't helped. I ordered a new switch from the Rubber Chicken Racing Garage and it should be here any day.

    As for the headlight. I did put a new bulb in and nothing changed. I've been spraying the switch on the left bar with WD-40 and contact cleaner. No joy.

    When the brake switch comes in, I'll remove the tank and dig deeper. I'll look at the grounds when I get it off. I really hate electrical problems!

    Thank you to everyone that made suggestions.
    #12
  13. Warin

    Warin Retired

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    More info on the headlight not working would narrow the problem.

    Is the low beam working? If yes then no problems with the ground nor the headlight relay (if it has one).

    Does the hi beam flash position get the hi beam to work? (the hi/low beam switch has 3 positions; low beam, hi beam and hi beam flash (spring loaded so you have to hold it there).
    #13
  14. rob

    rob Been here awhile Supporter

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    The high beam does not flash not does it light at all. I did try with both bulbs. The low beam works well.
    #14
  15. Warin

    Warin Retired

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    Ok, no ground involved as low beam uses the same ground. No relay involved (if standard - all bets off if someone has wired one or two in the original circuit).

    Check hi beam wire from left handle bar switch to globe .. there are at least 2 connectors in there - one at the headlight globe the other where the handle bar switch cluster connects to the main loom.
    #15