Results 1 to 11 of 11

Thread: 79 R100T Starting Problem...

  1. #1
    Registered User
    Join Date
    Jun 2012
    Location
    Hollis, NH
    Posts
    4

    79 R100T Starting Problem...

    Hello,

    I'm new here, this is my first post. :-)

    When I turn on the ignition, all the lights come up and the volt meter reads ~12V, transmission is in neutral, when I press the starter button: nothing happens, no clicking or anything. The only thing that happens is the brake failure light comes on, but my understanding is that is a check to make sure the bulb is working.

    I think the battery and starter switch are okay, I'm wondering is it might be the starter relay? I pulled it and it looks to be original and the contacts are in rough shape (corroded).

    Any help would be appreciated!

    Thanks,

    Chris
    79 R100T

  2. #2
    Administrator 20774's Avatar
    Join Date
    Sep 2005
    Location
    San Antonio, TX
    Posts
    12,868
    What does the battery voltage read with a meter across the terminals when you hit the starter button. If the voltage drops to below 10v, then it's the battery. If the battery doesn't change one iota, then you have to look upstream, like the relay. If the battery had any oomph to it, the relay should have clicked.
    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!

  3. #3
    Polarbear Polarbear's Avatar
    Join Date
    Jan 2006
    Location
    Clovis,CA
    Posts
    4,214

    Start easy:)

    The cables first, especially your ground cable to case. Its almost always the most simple things getting missed. My Airhead has fooled me too many times and I have to begin(remind myself) with the above idea , simple. Good luck, Randy

  4. #4
    Registered User
    Join Date
    Feb 2005
    Location
    EastDakota
    Posts
    108
    I'm just in the process of bringing a neglected 1979 R100T back to life. Same thing happened to me. All the lights worked except the neurtal light but it wouldn't fire. My neutral indicator switch is out so it will only fire if I have the clutch pulled in. What a sound after two years of sitting in the corner being ignored.

  5. #5
    Registered User
    Join Date
    Jul 2010
    Location
    Tularosa, NM
    Posts
    666

    Battery. . .

    Excellent tip from Kurt to check the battery when starter-loaded.

    I've chased the pernicious electrical demon hither-and-thither, only to find that "sometimes" an almost NEW battery was the culprit. NEVER assume that the battery is "good" just because some or all of the lights come on!

    I'm now an Odyssey fan, and have never yet had one fail me.

    Walking Eagle
    Last edited by Walking Eagle; 07-01-2012 at 03:30 PM. Reason: typo

  6. #6
    Registered User lkchris's Avatar
    Join Date
    Mar 2003
    Location
    Albuquerque, NM
    Posts
    4,726
    99% of the time it's the battery.

    Facts voltmeter reads 12V and lights come on are meaningless. In fact if the reading is exactly 12, that's low.

    Quickest/easiest test is to jump start it. If that works, it's the battery.
    Kent Christensen
    21482
    '12 R1200RT, '02 R1100S, '84 R80G/S

  7. #7
    Registered User
    Join Date
    Jun 2012
    Location
    Hollis, NH
    Posts
    4

    Follow up...

    Hi,

    Thanks for all the tips! With the help of one of my EE co-workers, I opened up the can on the relay and we found the failure: a broken wire on one side of the coil. I picked up a new relay (NAPA P/N: AR201), plugged it in, reconnected the battery and nothing, no lights or anything. I disconnected the battery, reinstalled the old relay (without the can), hooked the battery back up, turned the key on and got lights, etc. I closed the relay manually and the engined turned over no problem. I thought these relays were pretty common, but unless the one I purchased is defective (which is unlikely), there must be something different about it...? I don't mind buying the Bosh OEM relay, but I was hoping to avoid delays (my local BMW shop is off today, but I have plans to order a new relay from them tomorrow unless anyone knows a local source in Southern NH).

    Thanks,

    Chris

    PS: I measured 12V on the battery...

  8. #8
    Registered User
    Join Date
    Dec 2006
    Location
    Minneapolis, MN
    Posts
    97
    Follow the instructions here regarding using a generic relay in place of the bmw one.
    http://bmwmotorcycletech.info/slash5cricket.htm

    The one at napa should work if it is like this.

    http://www.oreillyauto.com/site/c/de...0381&ppt=C0335

    Just follow the instructions on snowbums site. You will also need some terminal connectors.

    Airhead Steve

  9. #9
    Registered User
    Join Date
    Jun 2012
    Location
    Hollis, NH
    Posts
    4

    Issue resolved!

    It turned out to be the relay. The one I purchased at Napa was "normally closed" and pin 87 and 87a were not common. The original Bosch relay is normally open and pins 87 and 87a are common. My EE buddy at work reworked the relay to behave the same as the original relay, he added a heavy gauge wire between pins 87 and 87a and insulated the outside contact near the coil. I plugged it in tonight and it fired right up. Thanks again for all your responses and tips.

    Chris
    79 R100T

  10. #10
    Day Dreaming ... happy wanderer's Avatar
    Join Date
    Mar 2010
    Location
    Vancouver, B.C. Canada
    Posts
    1,928
    Great you know what the problem is and got it running. I think however it would be a very good idea to replace that relay with a correctly configured normally open version. That circuit is wired N/O for a good reason!
    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

  11. #11
    Registered User
    Join Date
    Jun 2012
    Location
    Hollis, NH
    Posts
    4
    Yes, that's the plan, this relay is just temporary.

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •