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Thread: Headlight Issue '90 K75RT

  1. #1
    K75RT Keith
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    Question Headlight Issue '90 K75RT

    OK, I am officially frustrated with my 1990 K75RT! While in PA my headlight quit working. Replaced the bulb (H4 Halogen55/60 watt) and still nothing. Checked the High beam switch, cleaned with contact cleaner. Nothing. Pulled the tank, checked, cleaned and greased all the connections. Still nothing. Cleaned greased and reattached all the ground contacts I could find. Still no low or high beam. Got a new H4 connector and wired a switched power source off the power let. Low and High work fine off the the bypass.

    What else could cause this problem?
    Is there a factory installed relay for the headlight I missed on the wiring diagram?
    Ignition switch? But if that is the case why isn't the high beam working?

  2. #2
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    Quote Originally Posted by KKELLER149854 View Post
    OK, I am officially frustrated with my 1990 K75RT! While in PA my headlight quit working. Replaced the bulb (H4 Halogen55/60 watt) and still nothing. Checked the High beam switch, cleaned with contact cleaner. Nothing. Pulled the tank, checked, cleaned and greased all the connections. Still nothing. Cleaned greased and reattached all the ground contacts I could find. Still no low or high beam. Got a new H4 connector and wired a switched power source off the power let. Low and High work fine off the the bypass.

    What else could cause this problem?
    Is there a factory installed relay for the headlight I missed on the wiring diagram?
    Ignition switch? But if that is the case why isn't the high beam working?
    Did you check for current [at] the headlamp socket? When you do, check both [hot] 12V, and ground. If no current, then connections, fuse, relay, switch, broken wire.
    If no ground?..look for again, [an open] broken wire, bad connection @ a terminal, corroded wire , corroded terminal....

  3. #3
    Registered User kioolt's Avatar
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    There is a relay that is called the load relief relay. It's purpose is to cut power to all non-essiential for running loads when you are starting your bike. Non-essiential loads include the lights, radio, heated grips and so forth. That would have been the first place to check since it is a known problem.
    2004 R1150RT 145,700 miles
    1991 K100LT 126,700 miles
    1982 R100RT 106,900 miles
    Total 379,300 BMW miles

  4. #4
    K75RT Keith
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    Yes, I did check the H4 connector. Ground is good. I managed to get the high to function but only when the left switch was in the intermittent / flash position. No high in constant on position.

    The major issue at hand is that I have no LOW BEAM using the original connector. I went back and checked from the H$ connector to the terminal connector under the tank and have a good circuit to that point.

  5. #5
    K75RT Keith
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    Load relief relay

    How do I go about checking this relay?

  6. #6
    3 Red Bricks
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    The headlight switch can fail. The heat caused by the current going through the switch can cause the metal contacts to recede in to the plastic housing resulting in no continuity.

    In the future, please put the year and model of the bike IN THE TITLE. It helps us all.
    I've added that info for you.



    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
    Mine, Hers, Spare

  7. #7
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    Quote Originally Posted by KKELLER149854 View Post
    Yes, I did check the H4 connector. Ground is good. I managed to get the high to function but only when the left switch was in the intermittent / flash position. No high in constant on position.

    The major issue at hand is that I have no LOW BEAM using the original connector. I went back and checked from the H$ connector to the terminal connector under the tank and have a good circuit to that point.
    Check thoroughly the harness from the handlebar switch, to the junction at the main harness. Your on the right track, just haven't found it yet. And keep in mind, it still could be the relay.

  8. #8
    K75RT Keith
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    So the handlebar switch completes the circuit for the low beam, correct?

    If I'm reading the wiring schematic right, the low beam is controlled by the ignition switch. Should I be checking that too?

  9. #9
    3 Red Bricks
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    Yes and Yes. The light power goes through both the ignition switch and the light switch.

    I still think your problem is the light switch. You can pull the tank and check the power through the ignition switch to the connector for the left hand switch module to be sure you have power that far.

    Go to ibmwr.org for directions on cleaning/inspecting ignition switch and headlight switch.

    http://ibmwr.org/ktech.shtml

    Read this section:

    Switches

    Bypassing the K1100 Sidestand Switch - Bruce Keahey (January 2001)
    Cleaning the K Bike Ignition Switch - "Mr Bill" Wagaman
    Headlight Switch Repair/Cleaning - Don Eilenberger (April 1998)
    More on Headlight Switch Cleaning - Leo Horishny (September 1998)
    More yet on Headlight Switch Cleaning - Chris Bell (October 1999)
    Even more yet on Headlight Switch Cleaning - Paul C (July 2005)
    Ignition Switch Disassembly - Stuart Scott (April 1995)



    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
    Mine, Hers, Spare

  10. #10
    A bozo on the bus deilenberger's Avatar
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    Yes, I did check the H4 connector. Ground is good. I managed to get the high to function but only when the left switch was in the intermittent / flash position. No high in constant on position.
    ^^^^^^^^ BIG CLUE, points directly to the switch assembly. ^^^^^^^^^

    I'd add - after you replace the headlight switch (no one I know of has managed to fix one after the contacts melt into the body..) - consider adding a headlight relay setup. Eastern-Beaver (google is your friend) offers one that is basically plug and play with only minimal wiring needed.

    The stock switch was undersize for the stock headlight bulb. As soon as you start putting a higher wattage bulb in you're risking meltdown. The relays will not only avoid that, they'll improve your headlight output due to actually getting battery voltage to the bulb (which also makes bulbs last longer..)
    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
    3 Red Bricks
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    Quote Originally Posted by KKELLER149854 View Post
    I managed to get the high to function but only when the left switch was in the intermittent / flash position. No high in constant on position.
    I overlooked that tidbit of info. Yes, that really points to you needing a new switch!



    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
    Mine, Hers, Spare

  12. #12
    Registered User
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    Quote Originally Posted by KKELLER149854 View Post
    So the handlebar switch completes the circuit for the low beam, correct?

    If I'm reading the wiring schematic right, the low beam is controlled by the ignition switch. Should I be checking that too?
    For sure....and check the wire back [from] the headlamp [to] the switch.

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