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  1. #1
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    LED Trailer Lights flicker when truck is off

    Background is that I purchased a new tow vehicle. Since doing so, my trailer lights flicker rhythmically while the truck is off and it is parked in the lot at the lake. At first, I thought that it would quit after a while due to residual lights in the truck and the super-low voltage threshold needed to fire the LEDs. This is not the case, as it will still be blinking hours later when I return from fishing. For reference, this did not happen on my last tow vehicle.

    I know that this is caused by small amounts of voltage building on the truck's trailer wiring, but I'm not sure how to stop it. Is there a fix out there...a resistor kit or something that can be added between the truck and trailer? It's not enough current to drain my truck's battery, but it is a bit annoying.

    As I'm sitting here writing this, I'm wondering if it blinks in cadence with the security light on the dash??
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  2. Electrical/Wiring/Trolling Motors Moderator CatFan's Avatar
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    #2
    Can you tell if it is running lights, brake lights or both? What vehicle?
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  3. Member
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    #3
    2019 GMC Sierra AT4 and it appears to be all of the marker lights. I don't think that the brake lights blink. They blink once every 15-20 seconds.
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  4. Electrical/Wiring/Trolling Motors Moderator CatFan's Avatar
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    #4
    I would kind of guess it’s the system try to see if a trailer is connected. Does it do it with the truck running with the lights turned off?
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  5. Member
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    #5
    Not sure, I will have to check. Would it continue to check, even if the engine is off and the key is nowhere close? It does have the trailer light check system that will tell you if bulbs are out.
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  6. Electrical/Wiring/Trolling Motors Moderator CatFan's Avatar
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    #6
    Quote Originally Posted by MIZ-ZOU View Post
    Not sure, I will have to check. Would it continue to check, even if the engine is off and the key is nowhere close? It does have the trailer light check system that will tell you if bulbs are out.
    I wouldn’t think it should, but can’t imagine what else would be doing it.
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  7. Member
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    #7
    I’m having the exact same issue with a new 2019 Sierra. Did you ever find a fix?

  8. Member
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    #8
    So i have a 2019 GMC as well and my trailer lights flicker. It's part of the trailering package. The truck continuously monitors for the connection and flashes intermittently. If you disconnect the trailer harness from the boat when the truck is locked, i was told the alarm will go off. I havent checked that yet but that's what it is supposed to do. Hope that helps...

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    #9

  10. Member
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    #10
    Quote Originally Posted by dfrancom View Post
    A long but necessary read if you have a new truck. Used to be able to work on a truck without an encyclopedia of service bulletins.

  11. Member bhjr.'s Avatar
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    #11
    Some engineers do not know what real world conditions are. That's why these failures using electronics to monitor certain things exist and must be rectified. Just my 2 cents.

  12. Member
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    #12
    Google “trailer lights flicker” and you’ll see that various brands of trucks do this. My 2016 F150 also does it with a 2019 triton (EZ Loader) with LED lights behind it. I quit worrying about.