Tail Light Meltdown (FXSTC)

Discussion in 'Softail Models' started by UGSBUE, Aug 19, 2011.


    UGSBUE Member


    I own a completely stock FXSTC except for, foot pegs, foot control pads and luggage rack. i.e.: no mods to engine/exhaust or electrical of any kind.

    Model: Softail Custom (FXSTC)
    Year: 2008
    Mileage: ~23K

    I am seeking two things:

    1. Have you experiences a similar problem (described below)?
    2. Any thoughts/input regarding repair?

    Last weekend i had a melt-down of the rear wire harness connection inside the tail light housing. The melt-down (perhaps even a small fire) appears to have originated where the rear wire harness connects to the small circuit board that distributes current - via three seperate connectors - to the tail-light bulb, and the left/right turn signals (one connector for each).

    The melt-down (fire) completely destroyed the wire harness connector (the apparent source of heat/fire), the circuit board and each of the other three bulb connectors. In addition, heat/fire damage was caused to the license plate bracket to which the tail light is mounted as well as the tail light seal.

    I anticipate needing to replace the following:

    1. Rear Wire Harness
    2. Tail Light Circuit Board
    3. Tail Light Sockect/Connector
    4. Right Turn Signal Socket/Connector
    5. Left Turn Signal Socket/Connector
    6. License Plate Bracket
    7. Tail Light Seal

    Thank you for your consideration of my problem.
  2. glider

    glider Veteran Member

    What you describe could be the result of a chaffed wire to ground but that should pop the fuse. It sounds like the wiring is too far gone to determined if the wire was cut by some sheet metal or not. A poor connection in the plug can also cause heat to melt things too. You may want to check the output of your charging system as well.

    UGSBUE Member


    Thanks for the reply note. I owe a flash-back and explanation to appropriately frame maybe even end this short discussion.

    About two months ago i discovered that the brake light was illuminated only by the front (hand) brake and not by the rear (foot) brake. A very simple set of tests - based on a review of the circuit diagrams found in the Service Manual - found the root cause of the problem to be the rear-brake switch. For those who are not aware (i wasn't) the rear-brake switch is actuated by hydraulic pressure imparted by depressing the foot-brake pedal. In contrast, the front-brake switch is mechanical switch actuated at the hand-brake lever.

    I bought the new switch almost immediately from the local HD dealer for $19.03 including tax. I did not however replace the switch immediately...i am now hypothesizing that my procrastination may have precipitated the tail-light 'meltdown' as i have now replaced the switch (a one-hour job including a complete bleed/flush of the rear-brake fluid with new DOT 4).

    Here's my supposition - which i do not plan to validate: I tested the impedance of the new switch prior to installation to confirm that at its static-state the switch would be 'open' - no current flow - confirmed with a measurement of 'infinite' resistance. The same test of the old FAILED switch yielded high-resistance but a measurable value (i.e.: not infinite - 'open') indicating that some current was flowing through the FAILED OEM switch. I am hypothesizing that - although very low - electric current passed continuously through the FAILED OEM switch to the rear brake light. When combined with long rides and hot summer temperatures the current slowly caused the wire(s) to deteriorate as their design is not intended to carry continuous current. I believe the final meltdown was initiated during routine braking at a stop light wherein my wife first noticed an unusual 'electrical-like' odor. This would have sent the full amount of current from the hand-lever brake switch to the brake-light but the wire thickness was insufficient to handle it, sparks, combustion, meltdown.

    Please note that this is only a hypothesis based on a very simple impedance test of one component combined with visual observation of the area of the meltdown as compared to the connection of the rear wire harness to the main, etc. In addition, the entire electrical system appears to behave as normal with the rear wire-harness disconnected.

    The moral of the story is this: If it's broke - fix it - today. Problems can and will compound (snowball). Fortunately, the outcome of this did not result in injury and will only require several more hours and ~$180 of replacement parts to get back on the road.

    Thanks again for the input and feedback!

    UGSBUE Member

    There are no relays associated with the brake light circuit(s).

    UGSBUE Member

    Interesting...thanks for the schematic. It looks like the Relay has a connection to the ECM...i'm wondering, does your touring bike have cruise control as well (i believe that to be at least an option on touring bikes)?

    As i mentioned my brake-light circuits are quite simple 12vdc parallel circuit proctected by a single fuse - pretty much old-school power circuit.

    However, there's obviously an added degree of complexity when cruise control is a part of the bike's operational (even if just an option) condition. Namely, when the brake lever/pedal is squeezed/pushed a signal must be sent to [at a minimu] disengage the Cruise Control. That signal would have to be a part of the ECM's monitoring of the bike's operating status. Further, if the bike has anti-lock (not sure that was yet available in '08) the complexity of the ECM function is and requirement to "know" the rider's action with regard to braking - in addition to the status of wheel RPM - is paramount.

    Long-story short [again]: The relay is used - at least in part - to control the signal (on/off) to the ECM based on braking condition. I.e.: This all makes sense to me now....my ECM doesn't give a hoot about my braking status (no Cruise and no anti-lock).

    Thank you again...