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Thread: Tail light wiring question

  1. #1

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    Tail light wiring question

    I'm not a very smart guy. I don't understand the logic behind this magical trailer box thing. Can anyone tell me how to hook up the wiring to each of my my taillights? The picture depicts what I have. The light is an LED taillight. Thanks in advance.


  2. #2

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    On the To car side: The green wire connects to the white, Right Rear Turn, from the harness. The orange connects to the pink, Right Brake Light, from the harness. The yellow connects to a wire in the harness labelled Left Rear Turn. There is no need to connect the wire harness wire labeled Left Brake lLight.

    To Trailer: Green to the high power led on the right, yellow to the left.

    Ground wires connect to each other. Rear lights to low power leds.
    Last edited by Sigurd; 11-23-2018 at 03:30 AM. Reason: Spelling

  3. #3
    Senior Member Fixit's Avatar
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    The original setup (2 lamps/housings per side, each with dual filament bulbs) was configured to be 1 lamp/housing would do signal duty, 1 lamp/housing for stop duty - both would do parking light duty (dim filament).

    Swapping to the rectangles means the "bright" filament of the (now) single bulb/housing per side has to do both the turn & stop functions (no impact on parking light).

    The magic trailer box is a merger/traffic cop. It's "eavesdropping" on the L & R turn signal wires, and the common to both sides stop wire.

    The "stop" feed from up front is common to both sides of the car - hence only one input wire to the box. When there's voltage on this line it sends it straight through to the "bright" filaments of the lamp housings on each side using the (now) merged single "bright" output to each side.

    During a "stop with turn signal" scenario, there's voltage coming in on the "stop" wire, and (pulsed) voltage on the respective "turn" wire.
    This is where the magic happens...
    When it senses voltage on a given "turn" wire, it cuts the "stop" voltage input for that side, and allows the pulsed "turn" voltage through on the common output wire for a given side. When the pulsed turn voltage goes away (turn completed/switch off) it reconnects the stop voltage to the output wire.

    Make Sense??

    **There's a typo in Sigurd's connection explanation above...**

    The magic trailer box should probably be cut into the wiring at the back of the rear main harness where things split to the L & R of the car.
    You'll need to identify the Left Turn, Right Turn, and one of the Stop/Brake wires (doesn't matter which).


    In your case:
    The "To Car" green is spliced to the vehicle white feed wire (right turn)
    The "To Trailer" green is spliced to the leftover tail going to the lamp housing (Right side)
    The "To Car" orange is spliced to the vehicle purple feed wire (R Stop)
    (Clip and cap off the other "stop" feed wire)
    The "To Car" yellow is spliced to the vehicle L turn feed wire
    To "To Trailer yellow is spliced to the leftover tail going to the lamp housing (Left side)

    This should do it for you.

    You may have to exchange your traditional old-school thermal flashers (turn and hazard) for electronic versions. LED's don't pull enough current to heat up a thermal flasher and make it function - especially if you're replacing the fronts with LEDs as well.
    John D. - Minneapolis 'Burbs

    1965 El Camino - LT-1, 4L60e, 4wh discs, SC&C susp.
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  4. #4

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    It seems we of the 289 FIA family have struggled a bit with the trailer converter and the rear tail lights. It can be made to work but there is a much simpler and more elegant solution applied by Chris on his build that I utilized on mine. You can see it on his thread here: https://thefactoryfiveforum.com/show...ild-8833/page3. It's easy, inexpensive and it works. Joel

  5. #5

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    Quote Originally Posted by Sigurd View Post
    On the To car side: The green wire connects to the white, Right Rear Turn, from the harness. The orange connects to the pink, Right Brake Light, from the harness. The yellow connects to a wire in the harness labelled Left Rear Turn. There is no need to connect the wire harness wire labeled Left Brake lLight.

    To Trailer: Green to the high power led on the right, yellow to the left.

    Ground wires connect to each other. Rear lights to low power leds.
    Thanks Sigurd

  6. #6

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    Quote Originally Posted by Fixit View Post
    The original setup (2 lamps/housings per side, each with dual filament bulbs) was configured to be 1 lamp/housing would do signal duty, 1 lamp/housing for stop duty - both would do parking light duty (dim filament).

    Swapping to the rectangles means the "bright" filament of the (now) single bulb/housing per side has to do both the turn & stop functions (no impact on parking light).

    The magic trailer box is a merger/traffic cop. It's "eavesdropping" on the L & R turn signal wires, and the common to both sides stop wire.

    The "stop" feed from up front is common to both sides of the car - hence only one input wire to the box. When there's voltage on this line it sends it straight through to the "bright" filaments of the lamp housings on each side using the (now) merged single "bright" output to each side.

    During a "stop with turn signal" scenario, there's voltage coming in on the "stop" wire, and (pulsed) voltage on the respective "turn" wire.
    This is where the magic happens...
    When it senses voltage on a given "turn" wire, it cuts the "stop" voltage input for that side, and allows the pulsed "turn" voltage through on the common output wire for a given side. When the pulsed turn voltage goes away (turn completed/switch off) it reconnects the stop voltage to the output wire.


    Make Sense??

    **There's a typo in Sigurd's connection explanation above...**

    The magic trailer box should probably be cut into the wiring at the back of the rear main harness where things split to the L & R of the car.
    You'll need to identify the Left Turn, Right Turn, and one of the Stop/Brake wires (doesn't matter which).


    In your case:
    The "To Car" green is spliced to the vehicle white feed wire (right turn)
    The "To Trailer" green is spliced to the leftover tail going to the lamp housing (Right side)
    The "To Car" orange is spliced to the vehicle purple feed wire (R Stop)
    (Clip and cap off the other "stop" feed wire)
    The "To Car" yellow is spliced to the vehicle L turn feed wire
    To "To Trailer yellow is spliced to the leftover tail going to the lamp housing (Left side)

    This should do it for you.

    You may have to exchange your traditional old-school thermal flashers (turn and hazard) for electronic versions. LED's don't pull enough current to heat up a thermal flasher and make it function - especially if you're replacing the fronts with LEDs as well.
    Fixit
    Thanks for the detailed explanation. Now it makes sense to me. Unfortunately, I just found out that trailer box contraption is not compatible with LED lights but I was made aware of an inexpensive alternative that "cnutting" used in his thread.

  7. #7

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    Japollon
    Thanks for forwarding Chris's (cnutting) build thread link.

  8. #8

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    Chris
    I got your PM. Thanks for letting me know about the workaround. I just bought those diodes on Amazon and I'll ditch the trailer box thing.

  9. #9
    Junior Member
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    I have the same lights and a Trailer box will work but, it needs to be a powered unit. The one you have will not work.

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