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Thread: 2003 K1200GT brake light problems

  1. #1
    2009 F650GS SirRonny's Avatar
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    2003 K1200GT brake light problems

    Hi Everyone,

    I have a friend that has a 2003 K1200GT with Hannigan sidecar. He recently purchased a Hannigan trailer to go with it and this is the problem we ran into today.

    When the trailer is on the hitch and all lights wired up, everything works fine, except for the brake lights. When the trailer is plugged in, there are no brake lights anywhere, on the bike, sidecar or trailer. Unplug the trailer and the brake lights on the bike and sidecar work fine. So, we hooked the trailer up to my Jeep and all the lights, including brake, work just fine. We hooked it back up to the bike and everything worked again, except for the brake lights. So we unplugged the harness going to the sidecar and the bike lights, including brake, worked, as well as on the trailer. Hook the sidecar back up and no brake lights anywhere.

    My theory is that something in the servo ABS brakes is causing an overload condition, which is why the bike/trailer or the bike/sidecar combination work fine, but with all of them hooked up, nothing works.

    I hope this is clear, we looked at it so much today that I may be talking in circles. If so, ask away and I will try and clarify. Anyway, if anyone has ever ran into this before, I would appreciate any thoughts.

    Thanks in advance.

    Ron
    Ron Morris
    Cape Girardeau, Missouri
    2009 F650GS
    AMA, BMWMOA #153389, IBMWR and NRA

  2. #2
    rabid reader dbrick's Avatar
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    You've correctly ascertained that when the trailer and the sidecar are plugged into the bike, the lights don't work. If only the trailer or the sidecar is plugged in, the lights work. Thus, the problem is not an ABS servo issue, but instead is a ZFE issue.

    The ZFE body controller in the bike's CanBus network controls (among other things) the lights; various switches on the bike (like the ones on the brake pedal and brake lever) tell the ZFE what to do (like: "turn on the brake light"), and the ZFE then sends electricity directly to the bulbs. There's no connection between the switches you see on the bike and the lights that go on. The switches "talk" to the ZFE, and the ZFE "talks" to the lights.

    However, the ZFE has a built-in current limit to protect the bike's wiring from shorts: if more electricity than the ZFE's built-in limit tries to flow, the ZFE turns the circuit off. If less current is asked for when the circuit is again energized, the ZFE turns the circuit on again.

    I think wiring the bike + sidecar + trailer on the bike's original light circuits is asking for too much current. There's certainly enough juice in the battery and alternator to deal with the increased electrical usage, but the ZFE limit was apparently set so that it'll flow enough current for the bike, or the bike and trailer, or the bike and sidecar, but not enough current for the bike and trailer and sidecar.

    You'll need to use the low current flow that's permitted by the ZFE to actuate the primary coil on a relay, and have the relay's secondary connect the battery (through a fuse) to the electrical load that's too much for the ZFE - probably the trailer, perhaps the sidecar and trailer. You'll need two relays, one for the tail/running lights circuit, and the other for the brake light circuit. If the sidecar has a headlight, you might need a third relay (depending on what current limit the ZFE permits in the headlight circuit).
    David Brick
    Santa Cruz CA
    2007 R1200R

  3. #3
    2009 F650GS SirRonny's Avatar
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    Quote Originally Posted by dbrick View Post
    You've correctly ascertained that when the trailer and the sidecar are plugged into the bike, the lights don't work. If only the trailer or the sidecar is plugged in, the lights work. Thus, the problem is not an ABS servo issue, but instead is a ZFE issue.

    The ZFE body controller in the bike's CanBus network controls (among other things) the lights; various switches on the bike (like the ones on the brake pedal and brake lever) tell the ZFE what to do (like: "turn on the brake light"), and the ZFE then sends electricity directly to the bulbs. There's no connection between the switches you see on the bike and the lights that go on. The switches "talk" to the ZFE, and the ZFE "talks" to the lights.

    However, the ZFE has a built-in current limit to protect the bike's wiring from shorts: if more electricity than the ZFE's built-in limit tries to flow, the ZFE turns the circuit off. If less current is asked for when the circuit is again energized, the ZFE turns the circuit on again.

    I think wiring the bike + sidecar + trailer on the bike's original light circuits is asking for too much current. There's certainly enough juice in the battery and alternator to deal with the increased electrical usage, but the ZFE limit was apparently set so that it'll flow enough current for the bike, or the bike and trailer, or the bike and sidecar, but not enough current for the bike and trailer and sidecar.

    You'll need to use the low current flow that's permitted by the ZFE to actuate the primary coil on a relay, and have the relay's secondary connect the battery (through a fuse) to the electrical load that's too much for the ZFE - probably the trailer, perhaps the sidecar and trailer. You'll need two relays, one for the tail/running lights circuit, and the other for the brake light circuit. If the sidecar has a headlight, you might need a third relay (depending on what current limit the ZFE permits in the headlight circuit).
    Thanks for the reply David, I appreciate it. Would this have the Canbus system since it is a 2003? I didn't think the Canbus technology came along until 2005. Thanks again.

    Ron
    Ron Morris
    Cape Girardeau, Missouri
    2009 F650GS
    AMA, BMWMOA #153389, IBMWR and NRA

  4. #4
    Debbie's Servant Lee's Avatar
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    Quote Originally Posted by SirRonny View Post
    Would this have the Canbus system since it is a 2003? I didn't think the Canbus technology came along until 2005. Thanks again.

    Ron
    You're right, the 2003GT did not have Canbus. The next generation GT with the slant four engine did.
    Lee 2011 K1300S
    MOA # 30878
    Past BMW Bikes, 2003 K1200RS, 1991 K75S, 1987 K75T, 1984 R100RT

  5. #5
    2009 F650GS SirRonny's Avatar
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    Quote Originally Posted by Lee View Post
    You're right, the 2003GT did not have Canbus. The next generation GT with the slant four engine did.
    Thanks Lee, that is what I thought, but wasn't sure. With that being said, any ideas why the brake lights wouldn't work with everything hooked up?

    Ron
    Ron Morris
    Cape Girardeau, Missouri
    2009 F650GS
    AMA, BMWMOA #153389, IBMWR and NRA

  6. #6
    Debbie's Servant Lee's Avatar
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    Quote Originally Posted by SirRonny View Post
    Thanks Lee, that is what I thought, but wasn't sure. With that being said, any ideas why the brake lights wouldn't work with everything hooked up?

    Ron
    Sorry, I'm not much help when it comes to wiring.
    Lee 2011 K1300S
    MOA # 30878
    Past BMW Bikes, 2003 K1200RS, 1991 K75S, 1987 K75T, 1984 R100RT

  7. #7
    rabid reader dbrick's Avatar
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    Quote Originally Posted by SirRonny View Post
    Thanks for the reply David, I appreciate it. Would this have the Canbus system since it is a 2003? I didn't think the Canbus technology came along until 2005. Thanks again.

    Ron
    Looks like I had my years wrong and your bike is the earlier flat-four GT without CanBus. You should disregard my CanBus answer.
    David Brick
    Santa Cruz CA
    2007 R1200R

  8. #8
    Curmudgeon At Large Bobmws's Avatar
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    I have a similar setup. Start by checking the trailer output connector from the bike/sidecar. It sounds like you don't have the wiring correct going to the connector. Unplugged it wouldn't cause a problem, plugged into the trailer it's crossing a circuit somewhere.
    Bob Weis
    '04 K12RS - Hannigan Hack
    www.earplugco.com

  9. #9
    2009 F650GS SirRonny's Avatar
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    Thanks for the replies guys and I think he is going to take it into the dealer today and see what they can find. Sure is a mystery to me. Thanks again.

    Ron
    Ron Morris
    Cape Girardeau, Missouri
    2009 F650GS
    AMA, BMWMOA #153389, IBMWR and NRA

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