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My Lights at the Back of My Trailer will not go on

michaelroyymichaelroyy Member Posts: 30
in Battery/Electrical & Solar

What I hooked up my 2015 320 Boondock yesterday, the back lights would not work. I plugged a 7-pin tester into the back of my car (see picture plugged in & instructions), I couldn’t get it to light up with left signal +brake, right signal + brake… The only thing that was lit and stayed lit was the “BK” for the electric brakes. I am lost going forward and would appreciate any advice. Michael

7-pin tester.docx
7-pin tester instructions.docx
2015 Boondock
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    MuttonChopsMuttonChops Member Posts: 1,594
    links don't work for me.
    What is the tow vehicle make/yr/model?
    What brand/model 7-pin tester?

    '18 320 S,  pitched axle, 3020HE; PNW based
    TV: '17 Colorado V6 Z71 4x4, Tow Package, GM Brake Controller
    Adventures:  51   Nights:  322  Towing Miles 41,200+
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    michaelroyymichaelroyy Member Posts: 30
    Hope the attached works. 2020 Hyundai Sante Fe.
    2015 Boondock
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    rh5555rh5555 Member Posts: 487
    This sounds like a car, not a trailer problem.  I'd verify that by getting a friend with a tow-ready vehicle to come visit and plug the trailer into their vehicle.  If the trailer lights all work fine, then it's the car...
    Roger and Sue Hill | 2020 T@B400 Boondock (Cryst@bel) | 2022 Land Rover Defender 110 - P400 | San Juan Island, WA
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    pthomas745pthomas745 Moderator Posts: 3,653
    Clean the terminals on  both sides of the plug.

    2017 Outback
    Towed by 2014 Touareg TDi
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    MuttonChopsMuttonChops Member Posts: 1,594
    @michaelroyy ;  If appears, from web-searches, the 2020 Santa Fe comes from the factory with a 4-Pin trailer wiring connection point.  So someone has added the hitch receiver, 7-pin, and a brake controller.

    Normally the 7-pin aftermarket process is to Use the Factory 4-Pin Circuits and add a Brake Circuit and +12VDC (Battery) Circuit.

    Has your 7-Pin ever worked in the past?

    The Santa Fe uses one fuse to protect all the 4-pin light circuits;  Engine compartment fuse TRAILER 3

    Suggest you start by checking that TRAILER 3 fuse is not blown.

    If the fuse is not your issue, digging into how the 7-Pin was connected to your vehicle will be needed.

    Since the BRAKES (BK) LED is functional the aftermarket brake controller installation seems Okay.
    However the available documents are not clear on the +12VDC for the 7-pin.
    The +12VDC circuit might also be controlled by Trailer 3, or might not be    .

    '18 320 S,  pitched axle, 3020HE; PNW based
    TV: '17 Colorado V6 Z71 4x4, Tow Package, GM Brake Controller
    Adventures:  51   Nights:  322  Towing Miles 41,200+
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    michaelroyymichaelroyy Member Posts: 30
    Wow, thanks for the detail MuttonChops. In 2020 when I purchased the car, I had the hitch, controller, and the 7-pin all added at the same time by U-Haul. I purchased the trailer in 2020 and have used it without issue with this set-up. I will look at the fuses to see if that is the issue. Although I am not sure why the "BK" light would or could be on if I have blown a fuse? I will also look at the female connections to see if any are bent or dirty. Still learning... Thank you
    2015 Boondock
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    MuttonChopsMuttonChops Member Posts: 1,594
    michaelroyy said:
    . . . hitch, controller, and the 7-pin all added at the same time . . . purchased the trailer in 2020 and have used it without issue with this set-up. 

    . . . not sure why the "BK" light would or could be on if I have blown a fuse?
    Excellent that you have known history of everything Okay with your 7-pin.
    All the more to suggest the Fuse has blown.

    A typical aftermarket Brake Controller will have its own in-line fuse.
    The factory TRAILER 3 fuse is only for the lights and maybe +12VDC.

    '18 320 S,  pitched axle, 3020HE; PNW based
    TV: '17 Colorado V6 Z71 4x4, Tow Package, GM Brake Controller
    Adventures:  51   Nights:  322  Towing Miles 41,200+
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    MickerlyMickerly Member Posts: 352
    Many places have a trailer 7-pin tester. It plugs into the tow vehicle to check the two vehicle wiring. Even Home Depot had one. They appeal to go for $10 to $12. That will limit you problems to one vehicle or the other.
    2018 320CS-S
    "Just Enough"
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    michaelroyymichaelroyy Member Posts: 30
    MuttonChops

    My fuse set-up/diagram is much different than what you pulled off of the internet. Any further assistance would be appreciated. Michael
    2015 Boondock
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    MuttonChopsMuttonChops Member Posts: 1,594
    @michaelroyy ;
    Your Santa Fe has at least two Fuse Panels.
    The pictures you provided are the Instrument Panel Fuse box "S2010".

    You need to look at the Engine Compartment Fuse Box "S2020".


    '18 320 S,  pitched axle, 3020HE; PNW based
    TV: '17 Colorado V6 Z71 4x4, Tow Package, GM Brake Controller
    Adventures:  51   Nights:  322  Towing Miles 41,200+
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    michaelroyymichaelroyy Member Posts: 30

    OK. I think I have made significant progress, but still not all of the way there yet. Thank you MuttonChops for the head-start. I checked the fuse in the engine compartment, and it was good. I pulled apart the rubber connector (picture attached). The (3) wires connected to the 7-pin plug showed no resistance to their respective blades. All good. Then I followed the wires on the other side of the rubber connector into a plastic shrouding by the wheel well. I found a yellow rubber square that contained a 15 amp fuse (picture). When I tested it, it was blown. I replaced it. I also found a wire not attached. When I checked it for resistance inside the plug, it was the center two blades that showed no resistance. Looking this up, it appears to be an auxiliary/back-up lights. Not sure if this can be unattached and everything else is OK. I then ran one meter lead into the outgoing fuse blade (picture) and the other found no resistance to the right signal & brake (picture). Not sure why it happens to connect there. I put it all back together: new fuse and put the rubber connectors back together. Started the car, put on the left signal, and plugged in the 7-pin meter…nothing showing, but the 12 volt light. I am thinking of cutting off the rubber connectors on both set of wires and connect them individually to eliminate the possibility that this might be the problem. Any guidance would be appreciated. PS. I did test the 7-pin meter on my neighbor's car with the left blinker on and it blinked on and off in the right spot.


    2015 Boondock
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    MuttonChopsMuttonChops Member Posts: 1,594
    @michaelroyy;  Does sound like good progress.
    Hopefully your finding the +12VDC Fuse Holder to the RT Blade continuity on the 7-pin was just an operator error.  As probing into the 7-pin can get confusing/difficult.

    I've done additional research as well.  Your Santa Fe has an aftermarket 'Trailer Control Module'. U-Haul installed it and from the wire colors I can see it was sourced from e-trailer not Hyundai (which is fine).

    Point is the data you have provided suggests the Trailer Control Module has died.
    Why?
      - 1 -  With +12V Fuse fixed you now have +12V at the 7-pin.
     -  2 -  Your initial post stated the Brakes LED on tester worked.
     -  3 -  The car's trailer fuse is Okay.  Fuse that powers Trailer Control Module.

    Both the +12V and Brakes are part of the extra wiring U-Haul did originally.  Both work, while the Trailer Lights don't and they are only controlled by the Trailer Control Module.

    Suggest you use your voltmeter to measure the Voltages Between the Aftermarket 4-Pin pins and ground.  Expect none are working.  Replacing the Trailer Control Module is a doable DIY project.

    Reference diagram:

    P.S.  Very common for the backup lights wire not to be connected since NA trailers never have backup lights.
    '18 320 S,  pitched axle, 3020HE; PNW based
    TV: '17 Colorado V6 Z71 4x4, Tow Package, GM Brake Controller
    Adventures:  51   Nights:  322  Towing Miles 41,200+
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    michaelroyymichaelroyy Member Posts: 30
    Your the best MuttonChops. I will get my meter out again and check the controller. Can you recommend a unit or two to purchase on Amazon?
    2015 Boondock
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    MuttonChopsMuttonChops Member Posts: 1,594
    @michaelroyy ;
    If your 4-pin testing suggests the Trailer Control Module is bad - - -
    Before you order a replacement, suggest you remove the wheel well plastic cover,
    as at least one brand, Curt, aftermarket Trailer Control Module hides another in-line fuse under the cover.

    Amazon,  $40,  Curt
    { has a nice little video on installation }
    '18 320 S,  pitched axle, 3020HE; PNW based
    TV: '17 Colorado V6 Z71 4x4, Tow Package, GM Brake Controller
    Adventures:  51   Nights:  322  Towing Miles 41,200+
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    michaelroyymichaelroyy Member Posts: 30
    I took the plastic covering off to reveal the controller. I was expecting it to be plugged into an existing Hyundai plug. Instead, the Hyundai plug is somehow part of an individual wiring job. You can see the plug to the left on the attached picture. It is all corroded on the blades because it was never covered, so it has little use. The controller fell off its taped existence on the inside of the fender. I don't know how long it has been bouncing around, but I suspect the attached wiring and/or the controller are damaged. I suspect that the problem is in this area of the universe. I plan to take it to U-Haul, who installed the wiring and hitch, to have them install a new controller/harness. Sometimes I know when to say when. Thank you MuttonChops. This isn't the first time you have helped me out. 
    2015 Boondock
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    MuttonChopsMuttonChops Member Posts: 1,594
    michaelroyy said:
    . . . Hyundai plug is somehow part of an individual wiring job.
    . . . take it to U-Haul, who installed the wiring and hitch, to have them install a
            new controller/harness.
    Maybe U-Haul has a universal (wires only) Control Module so they don't have to stock a dozen different connector types.  Those 'cut wire, snap on' splices are common.

    Sounds like you have a Plan.  Glad I was of some assistance.
    Time now to pack my rig for a week of adventure.
    '18 320 S,  pitched axle, 3020HE; PNW based
    TV: '17 Colorado V6 Z71 4x4, Tow Package, GM Brake Controller
    Adventures:  51   Nights:  322  Towing Miles 41,200+
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    michaelroyymichaelroyy Member Posts: 30
    I will make a final post when I am up and running. It has been a good learning experience. Thanks for all of your help. 
    2015 Boondock
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    michaelroyymichaelroyy Member Posts: 30
    It turns out that the Control Module, that is glued to the rear wheel well, came unglued and just banged around while I was driving until it stopped working. A new module was installed, and I have my rear and side lights all working again. Thank you all for your input!!
    2015 Boondock
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