Results 1 to 7 of 7
  1. #1
    Member
    Join Date
    Jun 2012
    Location
    Jackson Tn
    Posts
    277

    Trailer wiring help

    Im looking for some help. Im trying to help out a buddy.
    Hes got a 2020 GMC 2500? Pulling a trailer with electric brakes. It originally has standard lights and were changing it over to LED. We may have more than one issue with it?
    We got the new LED lights installed on the older trailer. Hooked it up to the truck and just have brake and turn lights working. I need to add in here that the trailer had some king of small module, might be a resistor, that was not hooked up in the system at the time Ive not seen before? It had a red wire and not sure of the other color but since it was not wired up before Ive left it out of the system as well.
    Further checking with a test light I had no current coming out of the truck on the brown ( running light) wire. Checked the fuses and found no blown fuse? I then took another battery source and hooked to the trailer side plug checking to see if the lights burned. It then worked burning all functions. Running,tail lights, turn and brake lights. At this point the trailer seems to be good?
    Back to the truck.. past experience I know there is a module on the truck the trailer wiring goes thru. Maybe its an issue? Also Im wondering now if I should have checked voltage earlier with a meter instead of the test light? I did make sure the test light was working by the way. Ive had some experience where current was present but would not burn the light before. Then what about this other module that might be a resistor?
    Any suggestions appreciated!
    Mark Hopper
    Jackson Tn 38301
    htbboats@aol.com

  2. Member
    Join Date
    Jul 2009
    Location
    Benton, KY
    Posts
    4,944
    #2
    The module may be a breakaway switch. There should be a small battery in the system wired to the brake circuit. The breakaway switch would be hooked to the tow vehicle. If the trailer "breaks away" from the vehicle, the switch is pulled and the battery supplies power to the brake circuit to help stop the trailer.

  3. Member
    Join Date
    Jun 2012
    Location
    Jackson Tn
    Posts
    277
    #3
    Thanks for your response. I’ll look into that!
    Mark Hopper
    Jackson Tn 38301
    htbboats@aol.com

  4. Member wmitch2's Avatar
    Join Date
    Aug 2006
    Location
    Fresno, Ca
    Posts
    4,337
    #4
    Did you check the fuse's under the hood ? Also, check the connection of the brown wire on the truck plug if the fuse is ok.
    Ranger Boats / Mercury Motors
    G Loomis Rods / Shimano Reels
    Raymarine / MinnKota Ultrex
    Pepper Jigs / Robo Worms
    Troll Bridge / V-T2 Vents


  5. Member
    Join Date
    Apr 2012
    Location
    Insomnia, near Seaford Delaware
    Posts
    35,535
    #5
    Check the truck wiring to the round plug, the wiring goes by position on the truck, not color. Look also for a trailer fuse section in the fuse box.

  6. Member
    Join Date
    Dec 2018
    Location
    Kelseyville Ca
    Posts
    4,912
    #6
    Some trucks come with trailer fuse missing

  7. Member
    Join Date
    Mar 2015
    Location
    Georgetown, TX
    Posts
    82
    #7
    My GMC and past owned Chev have dedicated trailer fuses under the hood.