Trailer wiring connectivity issue

Discussion in 'Gen 3 Prius Main Forum' started by petersouth, Apr 4, 2021.

  1. petersouth

    petersouth New Member

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    I'm new to the forum.
    Like probably many of you, I didn't sign up until I had a problem.
    So here I am ..

    I have a 2013 Prius.
    Just purchased a brand new light utility trailer at Home Depot.
    I already have a trailer pigtail installed on the car. I've towed other trailers in the past with almost no issues.

    Problem: When I connected the car pigtail to the trailer plug - no Trailer tail lights.

    Attempted Diagnosis:
    Home Depot tech tested the car pigtail for power. Taillight, brake light and signal/hazards tested OK.
    HD tech tested the trailer independently using alternate power source (battery pack) wiring tester and the trailer taillight functions all tested OK.
    When we the connect the car pigtail to the trailer plug - NOTHING.

    At first, I thought it was just a bad plug end, but I think that is debunked by the fact the the testing equipment didn't seem to have a problem with either plug.

    Bottom line: Power at the Prius Harness tested OK
    and the Trailer taillights work independently, but when I connect the two - NOT OK.

    Any ideas?
    Baffled in Syracuse
     
  2. PriusCamper

    PriusCamper Senior Member

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    Maybe a bad ground wire? Or maybe trailer light brain is malfunctioning from too much load? How many lights on this trailer? Alot?

    Also, is the trailer light brain powered with wires that connect to 12v? Or just powered by tail lights?
     
  3. Georgina Rudkus

    Georgina Rudkus Senior Member

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    a748168d-48a2-4991-99b5-cfae61fd0930.__CR0,0,970,600_PT0_SX970_V1___.jpg If you live in Syracuse, NY, it would likely be a corroded connection. The usual method of connecting the tail light converter uses insulation displacement connectors on the very small 22 gauge wiring in the tail lights.
     
  4. BZzap!

    BZzap! Senior Member

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    I think you may need a special adapter for Japanese cars that are switched negative ground.
     
  5. PriusCamper

    PriusCamper Senior Member

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    That's one version... But each trailer light kit is slightly different. The better ones have that connection to the 12v but many versions do not.
     
  6. petersouth

    petersouth New Member

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    There are two taillights on the trailer.
    I believe they are powered by the Prius.
    Prius pigtail is connected to the battery located behind passenger side rear tire.

    My suspicion is that it has to do with grounding.
     
    PriusCamper likes this.
  7. petersouth

    petersouth New Member

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    I'm not sure what you mean.
    Are you saying that the trailer wiring is grounded in one way, and the prius cable may have been grounded in a way that is 'typical' for most vehicles, but incorrect for a Prius?
    I don't understand the concept of "negative ground."
     
  8. BZzap!

    BZzap! Senior Member

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    The concept is the ground is switched instead of the positive. In other words the is constant 12v current to the bulb filiment and it competes the circuit by using the ground through a switch.
     
  9. ChapmanF

    ChapmanF Senior Member

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    Is there any reason to think the Prius works that way?
     
  10. Yaesu

    Yaesu Junior Member

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    Some electrical devices in Japanese vehicles switch the ground to control the device. I have encountered horns and coolant fan thermostats that control the ground rather than the positive side of the circuit. But I have never seen lights are controlled by interrupting the ground. One of the most common problems with trailer wiring is a missing or poor ground on the trailer. You shouldn't be relying on the hitch to provide the ground. You need to be sure that the ground on the vehicle side of the connector is connected to a ground on the trailer side of the connector and the trailer ground needs to have a low resistance connection to each light.
     
  11. edthefox5

    edthefox5 Senior Member

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  12. Georgina Rudkus

    Georgina Rudkus Senior Member

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  13. Johnny Cakes

    Johnny Cakes Senior Member

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    The power windows in the Prius work like that -- the window fuse is an excellent source of constant 12v power. But we're heading off on a tangent.

    And reading between the lines, these other trailers in the past had lights and they worked? What were the "almost" no issues?

    You may be on to something with the plugs. Are the plugs wired exactly the same, wire-for-wire? Are you sure the actual connectors are making good connection with each other (not just the housings)?
     
  14. ChapmanF

    ChapmanF Senior Member

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    You'll generally find the fuse for every circuit to be on the +12V side of it, regardless of any other details of how the circuit works. (The window control circuits have an H-bridge kind of thing going on, so they can roll both up and down.)
     
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