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Thread: r90 Rear Brake Light - Always on

  1. #1
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    Question r90 Rear Brake Light - Always on

    My brake light indicator came on when I was riding home last night, checked the brake light and it is constantly on - as though I'm always braking.

    I did a little searching to see what was wrong, I pulled the lead off of the brake light switch on the main cylinder - the rear brake light is still on.

    What should I do to trouble shoot this further?

  2. #2
    Registered User mneblett's Avatar
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    Check the operation of the rear brake switch -- behind the right passenger footpeg plate -- and the wires from the switch back to the bike harness.

    Next, check the fluid level in the front master cylinder reservoir to make sure it is not too low, and then trace the wiring from the reservoir cap and the front brake switch back up -- look for abraded harness/wires and shorts to ground and/or between the reseroir cap and brake switch wires.

    Next place to look is inside the headlight bucket to see whether any of the wires plugged into the distribution board are shorted/fallen off their spades.

    Let us know what you find.
    Mark Neblett
    Fairfax, VA
    #32806

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    Still the same

    Thanks for the quick response - just got home and have checked some things out!

    took both wires off of the rear brake switch - brake light is still at its brightest. *I touched those two leads together and it stayed the same - still at brightest.

    Checked all the wires leading around the bike, to rear housing, to headlight bucket, to master cylinder, they all look good.

    Fluid in cylinder is good - checked the leads, they operate properly - brake indicator light goes on at the instrument panel when the float is activated

    The brake light indicator is not on when I start it, it does flicker sometimes when riding (could just be the master cylinder float?)

    All the connections in the housing and tail light look good.

    I'm at a loss, don't know what to do!

    Kevin
    R90/6 - 1976

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    When that happened to mine - it was the brake stop light switch (Part# 61 31 1 244 334) that failed 'on'. The tank has to be removed to access the switch. Simply unplug one of the two wires from the master cylinder pressure switch and see if that fixes the problem. If so, you need a new switch. Good luck!
    Stan

    AH# 13238

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    Should have mention this

    Hi Stan,

    I checked that too, pulled one of the wires off and the rear brake light didn't change at all.

    Kevin
    R90/6 - 1976

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    Question Short

    Does this mean I definitely have a short in the system and I'm jut not seeing it?

    Kevin
    R90/6 - 1976

  7. #7
    OldBMWMaster JDOCKERY132445's Avatar
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    Bulb

    My R1100RT did that for months and drove me nuts. It was the bulb.

    Buy a quality bulb...euro spec only.

    That cured my problem.

    Good luck.
    Jerry Dockery
    309 N. 3rd. Ave.
    Kure Beach, NC 28449
    1996 R1100RT main bike & 1985 K100RS...too fast to believe.

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    Quote Originally Posted by Aklo View Post
    Does this mean I definitely have a short in the system and I'm jut not seeing it?
    Based on the wiring diagram for a R90/6 (and pretty much all 1970-80 similar wiring diagrams) the brake light gets power through the rear or front brake switches and has a common ground with the turn signals. Any short would cause arcing and blow a fuse - not cause the brake light to stay on. Could anyone have done some re-wiring?

    It's not obvious from the wiring diagram about the fuse - but the headlamp contact plate with fuses shows the horn, turn signals, neutral light, and brake light all fed from the same voltage source. I would see if that fuse (15/8A) can be removed and if the brake light goes out. Maybe removing the fuse (feeding all the above mentioned lights and horn) can help verify your wiring matches that of a standard R90/6?

    Again, both brake switches supply power to the brake light and the ground is common with the turn signals. So, if neither switch is the problem or maybe the bulb as mentioned, then the wiring may have been modified. Start with the simplest things to check first. Good luck!
    Stan

    AH# 13238

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    Thumbs up Yes!

    It was the bulb in the tail light housing! works like a charm now! the ol bulb filaments looked good, the filaments were fine, must have been something internally.

    Thanks to all! Much appreciated! :Thumb

    Kevin
    R90/6 - 1976

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    Running Light on the Brake Light

    My tail light is still intermittent, usually in the not working position. I have a brake light, but no running light. I've replaced the brake light switch, on the master cylinder, with a new one. I have a multimeter, which I'm just learning how to use, when I read the green/brown wire and a ground wire I get reading of 3.3 - should this be 12? the bulb contact read 3.3 too. What else should I try?

    r90 taillight.jpg

    Kevin
    R90/6 - 1976

  11. #11
    Registered User lmo1131's Avatar
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    3.3 VOLTS? Yes, it should be 12V.

    Pop the headlight back out , and break the sub-frame harness connector (check for corrosion, etc. while you're there), and check the voltage. Personally... I'd use a 12V continuity tester for this job.

    Here's a thought. Just because the bulb is new doesn't necessarily mean that it's "good". Try another bulb?

    Last edited by Lmo1131; 12-23-2012 at 10:39 PM.
    "It is what you discover, after you know it all, that counts." _ John Wooden

    Lew Morris
    1973 R75/5 - original owner

  12. #12
    Registered User lmo1131's Avatar
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    FLASH!!! Something doesn't look right in your photo .... why is the brown (ground) wire connected to the contact that touches the contact on the bulb? The bulb is grounded through it's brass base to the housing, not by the contacts on the bottom of the bulb.

    Terminal #58 should be green/black EDIT > EDIT (gotta read my copy closer)> my bad, it appears that the tail light wire on the /6 is black/gray ( ? ) See > http://hstrial-wniglobalinc.intuitwe...R75_6_1975.jpg
    Terminal #54 should be green/red



    Last edited by Lmo1131; 12-25-2012 at 05:29 PM.
    "It is what you discover, after you know it all, that counts." _ John Wooden

    Lew Morris
    1973 R75/5 - original owner

  13. #13
    Monza Blue 1974 R90/6
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    Bingo! Good eyes.

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    rewired

    Definitely, good eyes! Thanks! Unfortunately, the running light is still not coming on.

    I used a 12 v continuity tester at the tail section on the wires at #58 and #54 - nothing.
    Checked it on the connector block (with wires still connected) and it lights up on #15 but not #58
    I do still have a brake light, but no running.

    Does this mean the wiring harness to the tail light has a short on 58 which is the running/license light?

    Thanks again.

    Kevin
    R90/6 - 1976

  15. #15
    Registered User lmo1131's Avatar
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    Does this mean the wiring harness to the tail light has a short on 58 which is the running/license light?
    Probably not a "short" to ground, or you'd be experiencing smoke and flames....

    So... do you have tachometer, speedometer, and parking lights? If yes, it's the bulb in the tail light assembly (just because one element is intact doesn't mean they both are).

    If not, it's probably the fuse at 58 (it feeds all of the above lamps).
    "It is what you discover, after you know it all, that counts." _ John Wooden

    Lew Morris
    1973 R75/5 - original owner

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