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Thread: 1971 R75/5-battery - starter

  1. #1

    1971 R75/5-battery - starter

    Just bought a decent R75. The starter switch worked when I bought the bike. The battery was bad, so I replaced the battery with a new one. The stater switch does not work now. I am wondering if I shorted out the system when removing the old battery and may have touched + and ! against the frame. I have kick started the bike a coouple of times since, but if I leave the power and ground connected to the battery, the battery goes dead over night. I am wondering if there is a bad ground or a dead short somewhere that is affecting both areas mentioned above. I have gone thru most of the exposed electrical connections, cleaned and reconnected, no improvement.

    Any tips or advise is appreciated. Also curious about switching the points/condenser system over to electronic ignition, again any info is appreciated.

    Thanks - gr82nz

  2. #2
    Registered User barryg's Avatar
    Join Date
    Aug 2003
    You can remove the 2 screws and pull the swithch out of the housing and spray some electrical contact cleaner on the mechanism. Might get it to work. It's worked for me.

  3. #3
    Liaison 20774's Avatar
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    Sep 2005
    San Antonio, TX
    Do you know if this battery dying problem existed before you bought the bike? I'm thinking this is an on-going problem. If it is, you'll need to monitor the battery voltage as you slowly unplug various electrical connections. Eventually, you'll find the circuit that is causing the drain and then do some detailed measuring of just that circuit.
    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
    #4869 DennisDarrow's Avatar
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    Jan 2006
    Sugar Valley, Ga
    Doubtful that you shorted anything out by grounding when you installed the battery.........In fact, with a good battery, when you touch the ground cable to the battery ground post, do you get a spark?............Definate indicator of a short........... just got this bike......what accessories have been installed in the last 30 years and had a chance to develop a short?..............For me, I would start with an ohm meter chasing circuits on the hot side looking for a ground short..........Especially on owner installed stuff..........

    Hope you understand what that means with the ohm meter chasing a ground..........

    I am of the if it aint broke dont fix it school of maintenance........Is something wrong with the points/ignition?...........

    God bless.....Dennis

  5. #5
    Registered User Anyname's Avatar
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    Jun 2007
    Portsmouth, NH
    Is it possible that your battery cables were damaged when you replaced the battery?
    BMW R bike rider, horizontally opposed to everything...

  6. #6
    I have experienced an open alternator rotor croaking the electric start function on a /5.

  7. #7
    Registered User kwb210's Avatar
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    Jul 2009
    Washington, the state
    I am of the if it aint broke dont fix it school of maintenance........Is something wrong with the points/ignition?...........

    God bless.....Dennis[/QUOTE]


    Points work on these airheads perfectly and for miles and miles when properly installed and adjusted, very simple. In fact i just changed mine out after nearly 20,000 miles for no other reason than um, well, there was no reason!
    1977 R100/7 1971.1972.1972.1973 R75/5
    1974 R90/6 multiple boxes
    Airhead Revival
    "Objects in the mirror appear to be losing" unk

  8. #8
    Thanks for the suggestions, plan to dig into it this weekend,

  9. #9
    Registered User DonTom's Avatar
    Join Date
    Jan 2011
    Auburn, CA, Reno & Cold Springs Valley, NV
    Quote Originally Posted by GR82NZ View Post
    Also curious about switching the points/condenser system over to electronic ignition, again any info is appreciated.
    I have had the Dyna Electronic Ignition in my 1971 BMW R75/5 for a good 25 years or so.

    And I have not checked my ignition timing for at least 20 years. No need. Just be sure the magnet thingie is on tight so it cannot slip out of adjustment.

    So just do it. It's well worth the money and time to install.

    -Don- SSF, CA

  10. #10

    R75 Electrical issues

    I went thru several circuits with the ohm meter and what I checked looked good.
    With further inspection I found a wire in the headlight that was corroded/disconnectet whcih I replaced. Thre is also a white wire that looks to be shorted out, but I cannot determine where it should be attached.

    I have attached a picture of the switch panel and the white wire situated straight right is the one in question. The Service manual that I have does not go into detail on this particular part.

    Any input is appreciated.

    Attached Images Attached Images

  11. #11
    --Tony AnnapolisAirhead's Avatar
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    May 2007
    Watkinsville, Georgia/Annapolis, Maryland
    Just curious, when you insert the ignition key, do you have the normal lights on the gauges?

    Does the bike crank but not start or just doesn't do anything? That info will be helpful.

    Aside from a potentially bad battery, you might want to inspect the condition of the battery cables (especially the positive side).

    On the headlight wiring, is the white wire from the headlight? If you follow the wiring from the headlight, there should be a yellow (low beam), white (high beam) and brown (ground) wire (see pic). That's the only white wire in a stock /5 harness that I know about.

    Also, does your bike have fuses inside the headlight? Some bikes were retrofitted with fuses. Extra farkles installed by the PO?
    Attached Images Attached Images
    Last edited by AnnapolisAirhead; 05-21-2011 at 02:45 PM.
    1971 BMW R75/5 | 1975 Moto Guzzi 850T Cafe | 1983 BMW R100RS | 1988 BMW R100GS
    1988 BMW K75 | 1998 BWM R1100RT | 2000 Moto Guzzi Quota 1100ES |2002 Moto Guzzi V11 LeMans

  12. #12
    Registered User ebeeby's Avatar
    Join Date
    Mar 2003
    McKinney, Texas
    Checking fuses is a good idea but you need to take that tank off and look at all the connections and you need to remove and re-seat the relays and check for corrosion. Wiggling the positive cable while putting in a new battery may have brought some corrosion into play. Pull the tank and check things out.

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