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Thread: mystery connection '77 r100rs

  1. #1
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    mystery connection '77 r100rs

    The black wire/connection pictured below is a mystery to me. All electrical components are working, but it appears it was connected at some point. The wire comes from the black junction pictured, and a black wire comes out the other side with a blunt end, which doesn't appear to have ever been connected to anything. I assume it's a ground, but should it be attached to any place special (battery, frame, etc.), or just grounded anywhere? If not already apparent, I have zero knowledge when it come to electrical issues. This is my last "button down" issue in the refurb of my 77 r100rs, so I want to get it right. Any guidance will be appreciated!
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  2. #2
    Benchwrenching PGlaves's Avatar
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    Do NOT attempt to connect it to ground!

    I see two black wires. The first one is at that connector.

    That is nothing OEM, and from all appearances it plugs into the shielded side of a standard SAE two-pole connector. Normally the shielded side would be the "hot" or +12v side.

    Take a test light or a volt meter; unplug the connector, and test for voltage inside the shielded side of the connector connected to those red wires.

    The second one has a ring terminal. I have no idea what it is but it is added accessory wiring of some sort.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
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  3. #3
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    I bought an '84 R100 in 1995 or so. The PO had installed extra brake lights, tail lights, driving lights, and assorted other crap. I pulled at least 10 feet of wire out of it after removing all the crap. Besides following PGloves advice, I would physically look to see where the other wires from that junction box go. I would also put some electrical tape on the bare end of the wire and the ring terminal just in case they are still hooked up to something.

    Lastly, the electrics of these things aren't rocket science. It takes patience more than brains to figure them out (a lot of patience sometimes -- I've had two real problems in my MC career. Both found me staring at the wiring diagram and tracing out power paths with a pencil for an hour or more. And both got solved). Check the wiring diagram for the color wires that go in an out of the junction box and see what they should be hooked up to.

    Edit: it looks to me like those wires head towards the tail of the bike. Any extra lights in the taillight?
    61 Gold Star, 76 R90S, 03 CBR600RR, '13 690 Duke, '14 Street Triple R

  4. #4
    Stage Crew beemerPhil's Avatar
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    Looks like it might be part of an accessory charger connection?



    Loose wires on a "previously owned" bike are generally suspicious- I'd be inclined to track it down and either make it work for whatever it was installed for or get it out of there. At least, if everything works without it, tape it off so it doesn't find it's own new home!

    Never assume anything about non-oem electrics!
    Phil Keppelman #20331
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    The shortest distance between two points.............
    ain't how I got here......

  5. #5
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    Thumbs up

    Quote Originally Posted by beemerPhil View Post
    Looks like it might be part of an accessory charger connection?



    Loose wires on a "previously owned" bike are generally suspicious- I'd be inclined to track it down and either make it work for whatever it was installed for or get it out of there. At least, if everything works without it, tape it off so it doesn't find it's own new home!

    Never assume anything about non-oem electrics!
    My father owned the bike in the late 70's and had a CB radio installed in one of the Krauser panniers. Probably the connection for that. I guess I'll tape it off. Thanks for the replies. 10-4 good buddy!

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