Wiring Non-Powered 3-to-2-Wire Splice-in Trailer Tail Light Converter with 4-Pin Wiring Harness

Discussion in 'Gen 2 Prius Accessories & Modifications' started by ydpplqbd, May 13, 2020.

  1. ydpplqbd

    ydpplqbd Active Member

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    I have a 2006 Gen2 Prius for which I am installing a trailer hitch. In addition, I intend to install a universal non-powered 3-to-2-wire splice-in trailer tail light converter with 4-Pin wiring harness. I am looking at the CURT 55178 converter.

    See:


    The CURT universal converter is the style of converter that I have used in all my vehicles for more than thirty years. So I would like to take a try at wiring this up.

    Q1. My question is: has anyone here installed one of these universal converters?

    Q2. If so, what was your experience installing and using a universal converter?


    PS I am aware that evnut has a website where he does this installation by modifying a 2002 Toyota trailer converter setup. See: Prius Trailer Wiring
     
  2. Minima Domum

    Minima Domum Member

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    Those plugs are strange to me, the ones we use in Australia are much bigger and more heavy duty...

    But regardless the installation should be pretty much the same, i would start by mounting the plug on the back somewhere near the tow ball, then run the wires through the grommet that's about half way up the bumper in the spare tyre well (pointing towards the back of the car rather than the ground like that tutorial shows). Then run the wires to their corresponding locations in the tail lights and solder them inline with the existing wires (an 'in place' wire stripper that can strip the middle of wires is great for this), plenty of electrical tape and cable ties to seal up the joins and make sure the wires are all tucked out of the way and voila, shouldn't take more than an hour at the most
     
  3. ydpplqbd

    ydpplqbd Active Member

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    I got most of the electrical install of the trailer harness started but I have run into a few snags as follows:

    1.) the brake light is an led assembly built into the tail-light assembly (I was unaware of this fact before starting this project) while turn signals and running lights are incandescent bulbs

    2.) I am using an unpowered 3-to-2 converter which is working with the turn signals and running lights but not working for the brake light.

    My theory is that the LEDs draw so that little power that the converter does not register the brake lights being actuated. My thought is put a resistor (AKA load resistors) between the draw from the existing running light wire and the converter. I am concerned about putting in too big of a resistor. Any thoughts of what size resistor to try.

    Or, alternatively, any thoughts on how to calculate what size resistor to use (I am thinking Ohm's law I=V/R)?

    PS Other thought was to use a transistor to act as a switch with existing running light tap triggering transistor and then isolated circuit with large resistor fed to the converter.
     
    #3 ydpplqbd, May 15, 2020
    Last edited: May 15, 2020
  4. ydpplqbd

    ydpplqbd Active Member

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    05152020_trailer_inputs_thick_final.JPG 05152020_running_light_thin.JPG Pictures attached here.





    Observations regarding wire colors of Gen2 Prius and its function as follows:

    brake light= green-with-white-stripe (at driver side white connector-thick wires)= blue (at driver side white connector -thin wires)

    running lights= solid dark green (at driver side white connector -thick wires)= brown (at driver's side white connector thin wires)

    left turn signal = green-with-yellow- stripe (at driver side white connector -thick wires)= green (at passenger side white connector - thin wires)

    right turn signal = green-with-yellow- stripe (at passenger-side/right white connector -thick wires)= yellow* (at passenger side white connector - thin wires)

    ground is at rear of spare tire well in the center (many other grounds already located here).

    *-best recollection on this wire color.
     
    #4 ydpplqbd, May 18, 2020
    Last edited: May 18, 2020
  5. ydpplqbd

    ydpplqbd Active Member

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    T-tap assortment ordered from Amazon. I used the red t-taps for this project.

    See:



    Pic attached of t-tap function.





    t-tap-connector.JPG
     
    #4 ydpplqbd, May 18, 2020
    Last edited: May 18, 2020
  6. Minima Domum

    Minima Domum Member

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    T-taps are horrible horrible devices and they need to go in the bin. Solder and heatshrink or quality tape is the only solid and reliable way to go.

    What does the 'converter' actually do? In every car I've ever dealt with apart from the really new canbus globe checking computer ones the trailer lights are just wired directly to the vehicle lights
     
  7. ydpplqbd

    ydpplqbd Active Member

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    [QUOTE="Minima Domum, post: 3037511, member: 183415"]T-taps are horrible horrible devices and they need to go in the bin. Solder and heatshrink or quality tape is the only solid and reliable way to go.

    Last car was wired with T taps for trailer harness. I am selling that car now and pulled the converter from that car and used it in my Gen2 Prius for this install. T-taps have performed for 12 years without any problems in my prior car. In the US, my experience is that used car buyers prefer a harness that has been tapped into with t-taps (rather than cut and soldered). Although, I agree with you that cutting and soldering is a superior way of connecting (but not of getting next buyer happy with a used car).

    ================================================================================
    What does the 'converter' actually do? In every car I've ever dealt with apart from the really new canbus globe checking computer ones the trailer lights are just wired directly to the vehicle lights[/QUOTE]

    In the Gen2 Prius there is a separate conductor for each of the following:

    a.) left turn signal;
    b.) right turn signal;
    c.) running lights; and
    d.) brake lights.

    In a base level US trailer using a "flat-four" connector, the conductors are as follows:

    i.) left turn signal (or brake light when brakes are applied);
    ii.) right turn signal (or brake light when brakes are applied); and
    iii.) running lights

    So when you have brakes applied AND, say left turn signal, then the following will occur:
    one filament in the left bulb will flash while one filament in the right bulb will stay lit solidly (to indicate brakes are applied).

    Converter makes it so that these two systems interface properly. I could go into greater detail but I am afraid that I would bore everyone to death.

    PS Wiring for "flat-four" trailers use a dual filament bulb (called an 1157 bulb). One filament has lower output than the second filament. Lower output filament is used for running lights. While high output filament is used for brake light and turn signals.
     
    #6 ydpplqbd, May 18, 2020
    Last edited: May 18, 2020
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  8. Minima Domum

    Minima Domum Member

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    Wow that's interesting, we have seperate bulbs for everything on trailers here the same as the vehicle, probably a bit more expensive overall but a lot more straight forward to wire and diagnose issues as well as clearer for drivers behind on the road
     
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