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Thread: Headlight wiring meltdown!

  1. #1
    Rally Rat warthog's Avatar
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    Angry Headlight wiring meltdown!

    This is what happens when you replace a 55w bulb with a 100w bulb on an 2002 1150 GSA. Your headlight wiring melts down because the circuit is not protected. Anyway I traced it back to the main harness and looks like it continued to melt inside the main harness.

    I am assuming I have to replace the main harness so I picked up a wiring harness for a 2001 GS of eBay for $115 and the part numbers match with the 2002 GSA. FYI dealer cost is $1500+.

    Looking for any advice or tips before I jump into this project.


    P.S. no I did not mean to put a 100w bulb in I should have grabbed my reading glasses before I installed the bulb. Getting old sucks

  2. #2
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    Wow !
    Its too bad those bulbs don't have different pin arrangements on them. Good luck wit,h the project.
    '03 R1150R, '03 F650GS, '97DR200SE,'78 Honda CT-90, '77Honda CT-90

  3. #3
    Registered User roger 04 rt's Avatar
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    I don't understand why only some of the circuits connected to the Load Relief relay are fused.

    The heated grips and horn circuits each have their own fuses, while the headlights (low and high beam) and corner lights (flasher) aren't. It doesn't seem to make sense.

    Then in 2004 BMW added a fuse to the high beam lamp but not the low beam.

  4. #4
    Registered User rxcrider's Avatar
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    How long did it take for this to happen? I've had a 100 W high H4 in my bike for most of this year and haven't had any issues. I only run the high beam at speed out of fear of overheating the lamp housing, but I haven't noticed any wiring issues. We are talking about a less than 10 A load @ 12 V. That isn't all that much.

  5. #5
    Curmudgeon At Large Bobmws's Avatar
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    Add relays to your headlights and a beefier ground wire. This is not a new issue on BMWs.
    Bob Weis
    '04 K12RS - Hannigan Hack
    www.earplugco.com

  6. #6
    Unfunded content provider tommcgee's Avatar
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    Go to the Eastern Beaver website and buy a relay harness for your headlight circuits. Tons of info there.
    Salty Fog Rally 2007, 2009, 2011, 2012, AND LOOKING FORWARD TO 2014!

    -Tom (KA1TOX)

  7. #7
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    Try reading the tables on current vs wire gauge for 12v then go look at the wire gauge in your bike.
    Essentially all German vehicles use wire at the low end of acceptable for the design loads including all current German cars and motorcycles that I've looked at.
    When you double the current, you're asking for trouble especially if there are any connrection issues- as there may well be on an old motorcycle that hasn't had its connections inspected and serviced as needed.

  8. #8
    Pepperfool GSAddict's Avatar
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    Add fuses to the 2 runs that are unfused.

    This is very easy to do if the harness is off the bike. There is a splice point for B+ inside the fuse box. One of the Red wires goes to the Load relief relay, fuse that one at 20A and the other one (Red) goes forward in the harness and feeds Ignition Switch, fuse that one at 10A
    I have done mine years ago when I realised the design flaw. Also have done others since then.
    If you use parts from your damaged harness you can have the new fuses in line with the original ones so the installation looks stock.

    Search this site for how to pictures thread as well as ADV riders.

    Here are some to start:

    http://www.advrider.com/forums/showp...9&postcount=12

    http://advrider.com/forums/showthread.php?t=665648

    http://www.bmwmoa.org/forum/showthre...ferrerid=31621
    Last edited by GSAddict; 11-10-2012 at 05:23 PM.
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    Ufda happens..........

    It's all about the details.

  9. #9
    Registered User GKman's Avatar
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    Quote Originally Posted by racer7 View Post
    Try reading the tables on current vs wire gauge for 12v then..
    I did exactly that before your post even. Found ampacity charts with a large variety of values. I'm most familiar with NEC but it isn't applicable for small wire sizes and is a very conservative rating. I'd be surprised of the lamp change posted would melt down a wiring harness based on ampacity alone. I would guess that over-current plus heat at the lamp melted the insulation near the lamp and shorted the conductors resulting in the meltdown.

    Anyone familiar with a wire chart applicable to vehicle wiring?

  10. #10
    Curmudgeon At Large Bobmws's Avatar
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    K bikes woud melt the plastic in the handlebar switch so the contacts would recess into the housing due to heat generated by the too small wiring, exacerbated by using a higher wattage bulb. Relays are a good thing.
    Bob Weis
    '04 K12RS - Hannigan Hack
    www.earplugco.com

  11. #11
    Outlander Omega Man's Avatar
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    That's a PITA. It's easy to overload a circuit by slowly adding more load to it. A good analogy would be an overloaded Christmas tree circuit. Another would be a toaster (essentially a dead short) calculated to glow without tripping a breaker (fuse).
    New pick-up trucks that are pre-wired with a load management system so the, for example running lights, fire the box under the hood which intern transmit the 12V to the trailer. This splits the load to 2 circuits. OM
    "Well they say.. time loves a hero but only time will tell.. If he's real, he's a legend from heaven If he ain't he was sent here from hell" Lowell George
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  12. #12
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    and for nearly the same money that will have been spent on the 100W bulb, and the repair of its aftermath, you could have gone HID, and had insane amounts of light, with less current draw than what was going on originally.

    just sayin'.
    Ride Safe, Ride Lots

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