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Thread: 78 R100RS Horn wiring

  1. #1
    Registered User STEVENRANKIN's Avatar
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    78 R100RS Horn wiring

    Quick question,

    I am having problems with my 78RS's horns.

    I see a horn relay listed on one wiring schematic, but not on another.

    I assume the two horn system uses a relay whereas the one horn system (not the RS) might not use a relay.

    Did in fact BMW RS models in 77 and 78 use a relay for the horns? I have not gone hands on the bike yet, just looking at the wiring schematics in advance and found the discrepancy.

    If there is no relay, it means either the horns or a horn is bad or the switch is bad. Not good if the switch is bad as they are NLA. St.
    Last edited by STEVENRANKIN; 03-26-2020 at 02:30 AM.

  2. #2
    Don't know, but I do know that when I put a second horn on my R75/6 I just wired it to the stock horn. Worked fine even without a higher amp fuse. YMMV
    '61 Clubman's Gold Star, '13 690 Duke, '13 Daytona 675R, '18 Street Triple RS, 2020 R1250R (gone but not forgotten: '76 R75/6, '84 R100, '76 R90S)

  3. #3
    Liaison 20774's Avatar
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    The BMW electrical CD shows just one relay for the R100RS twin horn setup.
    Kurt -- Forum Liaison ---> 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!

  4. #4
    Registered User STEVENRANKIN's Avatar
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    Thanks

    I knew instinctively the two horn RS and RT bikes have a relay whereas the single toot toot horn bikes may not.

    I am just surprised I have a wiring schematic for a 78 bike that does not show the relay and one that does.

    I will err on the side of common sense and look for a relay when I go hands on with the bike.

    Really can't be a whole lot wrong. St.

  5. #5
    B Reams brook.reams's Avatar
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    Quote Originally Posted by STEVENRANKIN View Post
    I knew instinctively the two horn RS and RT bikes have a relay whereas the single toot toot horn bikes may not.

    I am just surprised I have a wiring schematic for a 78 bike that does not show the relay and one that does.

    I will err on the side of common sense and look for a relay when I go hands on with the bike.

    Really can't be a whole lot wrong. St.
    Steve,

    The '77 & '78 RS have the horn relay. It is located on the left spine tube and plugs into the bracket that includes the starter relay. The Horn relay is the front one.

    Starter & Horn Relays and Sockets

    Horn Relay (Right) Starter Relay (Left), From Top

    Best.
    Brook Reams.
    Brook Reams - Arvada, CO
    Endeavor to Persevere
    Various Two-wheeled Vices, All BMW || Website: Airhead Rebuild Projects
    2004 R1150-RS||2002 F650-GS||1983 R100RS||1977 R100RS||1973 R75/5

  6. #6
    Registered User STEVENRANKIN's Avatar
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    Just confused

    I was just confused as to how I could have two wiring schematics showing me two different things.

    Turns out, one of the schematics is wrong. In the trash it goes.

    Turns out the switch is bad. Moto bins in the UK had one in stock. Of course now, Max is listing one again on their site. They were supposed to be NLA, someone is making them again or someone found a batch.

    I really would like to see them being made again along with a lot of other NLA parts. Cheers all, St.

  7. #7
    Liaison 20774's Avatar
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    St -

    When was your RS made? I believe the part number is 61 31 1 373 585...is that what you found? Sites suggest that it has been superseded by -588. I have some notes squirreled away that provide alternatives to the BMW relay. Some were VW/Audi parts...also Hella parts. Sometimes the non-BMW relay doesn't have all the features. Also, RealOEM indicates the part was used in the car line.

    Interesting that RealOEM shows a gap between 6/77 to 8/78 for the R100RS...suggests that no bikes were built in that timeframe. However the BMBikes engine listing site suggests otherwise.
    Kurt -- Forum Liaison ---> 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!

  8. #8
    Registered User STEVENRANKIN's Avatar
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    My RS

    My 78 RS is a Euro spec bike which has the switch on the left handle bar for horn, and head light off, park and on. High and low.

    I see now the switch is again available or at least listed at MAX. I ordered one from Motobins. St.

  9. #9
    Registered User STEVENRANKIN's Avatar
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    I got to learn to read

    OKay, I have to learn to read.

    Max does not have the switch I need, it IS NLA.

    It also looks like I ordered the wrong switch from Motobins.

    Not going well here. Sorry for the confusion. St.

  10. #10
    Registered User STEVENRANKIN's Avatar
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    Continuing the story if you are interested

    So, the switch I need is NLA. However, there may be a slim chance one exists new and Megan at Kissel's is checking for me. If not, I will have to purchase the current switch without the headlight off, park and on switch.

    I have found out things assembled in a factory with the proper jigs and tools do not always present themselves as best candidates for home repair.

    My current switch is case in point. Smart fellow me, looked at it and thought "a ha, I can pop that little c-clip on the headlight switch and take it apart to clean the contacts."

    All was well until the teeny tiny detent ball bearing and its retaining spring went over my shoulder. I did manage to find them however after the fourth try to put them into place without the proper jigs and tool, they went for a walk and are now gone.

    Moral of the story, "Do not mess wi thing ye ken nothin about!" St.

  11. #11
    Registered User jad01's Avatar
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    If you have to purchase/install the US handlebar control switch:

    There use to be a tech article on the IBMWR site that showed how to wire in an auxiliary on/off switch for the headlight that turned off the main lamp while leaving the parking light illuminated. When auxiliary main switch is "on", the headlight switch on the handlebar works normally. I did it on my /7 maybe fifteen years ago, mounting a marine style toggle switch in the fairing. It works great and was easy to do. I looked on the IBMWER site to see if the article was still there, but I don't see it. I probably printed the instructions when I did it- if I can locate them, I'll post a copy.
    Jim (MOA 83200)
    '78 R80/7 (Anastasia) and '84 R100RS (The Millennium Falcon), '86 K75C (Icy Hot)
    '90 and '93 Mazda Miatas (Jelly Bean and Red Hot), '97 Nissan XE PU (Mighty Mouse)
    '96 Giant Upland (big Kendas, baby!)

  12. #12
    Registered User STEVENRANKIN's Avatar
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    Used

    Well, I found a good used switch.

    I won't be taking it apart. St.

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