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Thread: K75 intermittent cherging light when > 3500 RPM

  1. #1
    Phlyin' Phil
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    K75 intermittent cherging light when > 3500 RPM

    My '86 K75 has had an increasingly 'on' charging system light. The light almost never comes on and stays on. Over 3500 RPM makes it go on and off, and hitting a large bump at that time tends to make the light come on. When above 3500 RPM and getting the light on/off, sometimes the motor cuts out, making a flat sound, then picks back up.

    I've started it and checked the alternator output by putting a volt meter across the battery terminals and even when I put the emergency flashers on and make the brake light come on, voltage stays up around 13V. So I think the alternator is working fine.

    I checked the ground with the bike off (battery ground to motor or other connected metal part) and ground (while the bike is sitting still) seems fine.

    Are there usual suspects for connections to start with when trying to find this type of problem?

    Any help is appreciated,

    Phil Rogacki
    p_rogacki@hotmail.com

  2. #2
    Happy to be here! :) The_Veg's Avatar
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    Hmm, I don't know if this is the same problem but I've heard of charging system lights on K-Bikes dimly glowing with the intensity increasing with RPM. The glowing I describe is known to be a non-problem, just a fluke of the circuit. A fix is available by installing a diode somewhere I forget. See the tech article at www.IBMWR.com for details.
    Of course if your bike's problem is not that then I don't have any ideas...

  3. #3
    Blocking the slow lane
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    I'm not an electrical troubleshooter at all, but if I had a 17-year old bike in front of me with that weirdness going on, I would get the gas tank and seat off and start trying connections under the tank, as well as un-plugging and re-plugging connections in the relay box. The situation that you describe sounds like there is a loose connection that starts to fail as the vibes from 3500rpm creep in, so un-plugging and re-plugging stuff might turn up a simple fix like a partially loose connector. Don't forget to check that big plug on the alternator....that is probably where I would start first.
    Jon Diaz
    BMW K75/K12GT
    BMWMOA Ambassador

  4. #4
    Have bike, will travel lancew's Avatar
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    The "flat" sound is the motor trying to run w/out benefit of a fuel pump- I heard that sound on my '85 K as it rolled to a stop... in a construction zone... with no breakdown lane... at night... leaning against the Jersey barriers with 18-wheelers going by about 8 inches from my left elbow. I have never been so scared. I sweat right thru 2 shirts and a riding jacket... no kidding, I thought I was gonna get smooshed.

    I would remove your tank and clean ALL your connections thoroughly, then apply dielectric grease when you re-attach. Loose connections will only get looser. My uneducated guess is that JDiaz is on the right track about checking the alternator first, but as long as you are in there, might as well do them all.
    #92115 - '01 R1150GS

    Why don't they make a Nerf Martini Glass?

  5. #5
    Blocking the slow lane
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    Geez Lance, I broke out in a sweat just thinking about you sitting in the construction zone with a broken bike. Yow!
    Jon Diaz
    BMW K75/K12GT
    BMWMOA Ambassador

  6. #6
    Have bike, will travel lancew's Avatar
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    Wouldn't wish it on anybody... coincidentally, that was the day I stopped ignoring "little" problems.

    #92115 - '01 R1150GS

    Why don't they make a Nerf Martini Glass?

  7. #7
    Phlyin' Phil
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    Thanks, everyone, for your input. I will get the dielectric grease and start going through the connections as soon as I can. When something works, I'll post it here.

    Phil

  8. #8
    A bozo on the bus deilenberger's Avatar
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    Originally posted by progacki
    Thanks, everyone, for your input. I will get the dielectric grease and start going through the connections as soon as I can. When something works, I'll post it here.

    Phil

    Ummmm... Phil, dielectic = doesn't conduct electricity. I much pefer clean bare contact, or contacts enhanced with Krytox (which is what BMW recommends for the cars.. it is priced up there with exotic drugs - about $50/ML..)

    It's available from NAPA car parts dealers - luckily a tiny bottle of it goes a LONG ways. I used it on every contact on THE K75S when I replaced the wiring harness (another story..) and have experienced no wacky (tech-term) electronics problems since then.
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders New Sweden BMW Riders
    '07 R1200R (current ride) and some bimmers.. and a Porsche

  9. #9
    Have bike, will travel lancew's Avatar
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    Originally posted by deilenberger
    Ummmm... Phil, dielectic = doesn't conduct electricity.
    No, but it does a great job of keeping air and moisture out of contacts once you've cleaned 'em. Especially with old wiring, anything you do to keep it from fouling at the connectors is a good idea. Good for accessory sockets too.
    #92115 - '01 R1150GS

    Why don't they make a Nerf Martini Glass?

  10. #10
    A bozo on the bus deilenberger's Avatar
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    Originally posted by lancew
    No, but it does a great job of keeping air and moisture out of contacts once you've cleaned 'em. Especially with old wiring, anything you do to keep it from fouling at the connectors is a good idea. Good for accessory sockets too.
    I guess we'll just have to agree to dissasgree. I won't put an insulating grease on connectors on my bike. When I do lubricate electronic connectors (and I used to do this kind of stuff for a living), I'll use a conductive grease, selectively applied to enhance conductivity.
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders New Sweden BMW Riders
    '07 R1200R (current ride) and some bimmers.. and a Porsche

  11. #11
    Have bike, will travel lancew's Avatar
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    The DG is just to protect the connections and inhibit corrosion, it's pretty common practice in applications where exposure to weather, temperature changes and harsh conditions are the norm, especially when the wiring can go a long time without much attention. Heavy equipment, OTR trucks, marine junk, all kinds of trailers. It really does make a difference. I guess I've never given much thought to conductivity- if it ain't working I just scrape the shiny parts harder .

    Isn't Krytox the DuPont stuff? That's supposed to be some kind of miracle lube if it's what I'm thinking of, temp resistant plus chemically inert and lasts forever- would certainly be up to the task of protecting a wiring harness.

    "I guess we'll just have to agree to dissasgree"- fat chance, pal. I absolutely refuse to disagree...

    regards,

    Lance
    #92115 - '01 R1150GS

    Why don't they make a Nerf Martini Glass?

  12. #12
    Happy to be here! :) The_Veg's Avatar
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    Have to agree with Lance- the physical connection is better than any other conductor thrown in the middle. The grease basically makes an insulator around the point of connection to keep that point from being fouled, and protects the contact surfaces when they are open. The grease gets squished out of the way when they are closed. It's worked for decades.

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