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Thread: why does the tail light quit working when the turn signal stops working?

  1. #1
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    why does the tail light quit working when the turn signal stops working?

    I'm wondering why this is so, as it doesn't seem like a good idea.

    I can't think of any reason why the tail light/brake light should be wired into the turn signal relay, and yet, sure as gravity, when my turn signal relay dies (Which happens with annoying regularity. I'm averaging a relay a year), my tail lights quit working.

    Why is this so?

    EDIT: A brief perusal of the wiring diagram reveals no clues either. In fact, I don't see where the wiring connects the two, which confuses me even more.

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    Administrator 20774's Avatar
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    What bike are you talking about? Probably a research of the appropriate wiring diagram might have some clues.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

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    1977 R75/7

    Stock electrical harness.

    And, as I said, they don't -seem- to connect.

  4. #4
    James.A
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    The common lighting connection on the back end of a /7 (or any airhead I am familiar with) would be the brown wire, which is ground.

  5. #5
    Registered User lmo1131's Avatar
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    I can't think of any reason why the tail light/brake light should be wired into the turn signal relay
    And it shouldn't be.

    Since you started the Sourcing Wire thread, I'm gonna go out on a limb and guess that your wiring harness is a mess...

    If your TAIL LIGHT is going out when your T/S RELAY fails it must be receiving power from it - and it should not be.

    The TAIL LIGHT circuit (main block terminal #58 (Black/Gray)) also powers the INSTRUMENT LIGHTS, the CLOCK and VOLTMETER lights, and the PARKING LIGHT (in the head light. Do these lights also fail when the T/S RELAY goes south?

    A BLACK/GRAY wire should be connected to terminal #58 ON THE TAIL LIGHT. If it is not, what color is?

    ... my tail lights quit working.
    You only have one tail light, right? The turn signals are not both steadily illuminated at the same time... ? Correct?

    edit - See if your TAIL LIGHT terminal #58 is somehow connected to T/S RELAY terminal #49a (not 49). 49a (GREEN/YELLOW) powers the turn signal switch on the handlebar perch.

    I hate burning up the bandwidth, but it helps to see the diagram.

    Last edited by Lmo1131; 02-14-2013 at 08:17 PM.
    "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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    I'm going to do a more in-depth digging, but as of right now..

    1. the tail light/brake light fail when the blinker relay is removed.

    2. the blinker will only blink for so long, before it stops blinking for a little while. If shut off, it starts working again in 5-10 minutes.

    3. The blinker indicator will fail if left on for too long. THis too, resumes function, if left off for a while...

    I will post more, as I have more.

  7. #7
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    I would also be looking into why your t/s relays keep getting killed (which is different than just "dying".) Something is not right there- if i think back on it, i have had exactly ZERO t/s relays die on a m/c in the last 35+ years.
    Ride Safe, Ride Lots

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    I suspect the two are related.

  9. #9
    Registered User lmo1131's Avatar
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    1. the tail light/brake light fail when the blinker relay is removed.
    The TAIL LIGHT and BRAKE LIGHT should receive power from two separate terminals on the main contact plate inside the headlight housing. If they do not come on when the RELAY is removed it is because they are receiving power from the RELAY circuit - which is incorrect.

    The TAIL LIGHT > from terminal 58 (gray/black wire; on the contact plate in the head light) which is energized by the gray wire when the ignition switch (terminal 58) is turned on.

    The BRAKE LIGHT > terminal 15 (green/black wire; on the contact plate in the head light) which is energized by the GREEN wire when the ignition switch (terminal 50) is turned on. The GREEN/BLACK wire feeds the front and rear brake light switch - the wire(s) coming out of the two switches are GREEN/RED and go to the BRAKE light terminal 54 in the housing.

    2. the blinker will only blink for so long, before it stops blinking for a little while. If shut off, it starts working again in 5-10 minutes.
    Your RELAY is overheating and failing (again).

    3. The blinker indicator will fail if left on for too long. THis too, resumes function, if left off for a while...
    The INDICATOR is fed directly from the RELAY by a BLACK/WHITE wire which is connected to terminal KBL on the RELAY. If the INDICATOR LIGHT is failing it's because the RELAY is failing.

    The TAIL LIGHT circuit (main block terminal #58 (Black/Gray)) also powers the INSTRUMENT LIGHTS, the CLOCK and VOLTMETER lights, and the PARKING LIGHT (in the head light).
    Do these lights also fail (go out) when the T/S RELAY goes south or is disconnected?

    Have you opened up the headlight housing and taken a look at the contact plate to verify correct connections per the wiring diagram?
    "It is what you discover, after you know it all, that counts." _ John Wooden

    Lew Morris
    1973 R75/5 - original owner

  10. #10
    Day Dreaming ... happy wanderer's Avatar
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    Quote Originally Posted by Lmo1131 View Post
    And it shouldn't be.

    Since you started the Sourcing Wire thread, I'm gonna go out on a limb and guess that your wiring harness is a mess...

    If your TAIL LIGHT is going out when your T/S RELAY fails it must be receiving power from it - and it should not be.

    The TAIL LIGHT circuit (main block terminal #58 (Black/Gray)) also powers the INSTRUMENT LIGHTS, the CLOCK and VOLTMETER lights, and the PARKING LIGHT (in the head light. Do these lights also fail when the T/S RELAY goes south?

    A BLACK/GRAY wire should be connected to terminal #58 ON THE TAIL LIGHT. If it is not, what color is?



    You only have one tail light, right? The turn signals are not both steadily illuminated at the same time... ? Correct?

    edit - See if your TAIL LIGHT terminal #58 is somehow connected to T/S RELAY terminal #49a (not 49). 49a (GREEN/YELLOW) powers the turn signal switch on the handlebar perch.

    I hate burning up the bandwidth, but it helps to see the diagram.
    May I ask where these colour diagrams are from? I have the B/W ones from PowerBoxer.de linked to from Snowbums site but they are blurry and difficult to read. I am looking for schematics like these for my 1982 R100RS.
    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

  11. #11
    Registered User lmo1131's Avatar
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    Soytenlly!

    They have been curated by our friend, benefactor, and Forum Administrator Kurt (aka: 20774) in the MOA Resources and Links section found at the bottom of the "The Garage" section.

    '82 R100
    "It is what you discover, after you know it all, that counts." _ John Wooden

    Lew Morris
    1973 R75/5 - original owner

  12. #12
    Day Dreaming ... happy wanderer's Avatar
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    Quote Originally Posted by Lmo1131 View Post
    Soytenlly!

    They have been curated by our friend, benefactor, and Forum Administrator Kurt (aka: 20774) in the MOA Resources and Links section found at the bottom of the "The Garage" section.

    '82 R100
    Now why didn't I look there?

    Thanks! These are so much easier to read. I keep telling the eye doc there is nothing wrong with my eyes, I just need longer arms!
    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

  13. #13
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    Lew refers to Stephen Bottcher's page which has quite a few diagrams. Snowbum also has some diagrams, but I don't think they're in color, at least not most. The diagram that Lew references above in his post is from a we'll maintained website that is mostly about the 1978 models, but has quite a few other interest articles and brochures. The diagram that was posted is about half way down this page:

    http://www.omnilex.com/public/bmw78/

    While no diagram is 100% correct, this diagram should be applicable to the '77 /7 in question...except for the cable-drive tach!
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  14. #14
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    ok, upon some investigation, it would seem my ignition switch is miswired.

    However, instead of having pins 30,30,50,56 ,58 on the back of the switch, I have ( in order) 15, 30, 30, 58, in a row, with pin #56 above the row, in the 11 o'clock position.

  15. #15
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    Symptoms persist.

    Blinker blinks very fast, and the blinker light on the dash does -not- light up.

    Gauge lights extremely dim.

    When in the 'park' position, tail light comes on.

    when in the run position, tail light goes out, but brake light works.

    Tail light comes back on if you turn the headlight on, and brake lights work.

    when the turn signal module is unplugged, tail light/brake light now function.

    I"m not sure what I did, but it seems to be working now.

    I suspect that my wiring harness is due for a change.

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