more trailer wiring

Discussion in 'Chevy Suburban Forum (GMC Yukon XL)' started by Diceman, Jul 24, 2007.

  1. Diceman

    Diceman Member

    i finally went outside and tested the wiring. synopsis of the problem is that the wiring works, but i randomly blow tail light fuses. replace them and it works fine, even with the trailer plugged in. a few days later though, i notice the lights arent working again. it is always after the trailer has been plugged in.

    here is what the manufacturer of the trailer has to say about the wiring.


    my LT, RT, and GND are correct. when i use the brakes i get +12 on the running lights, when i turn on the running lights, i get -12 (however that happens), if i use running lights and brakes lights at the same time, i get 0. i dont get readings on the LT and RT when i use the brakes like i figure i should.

    i bought a harness for the truck so this is plug N play right now. do i need some type of converter?

    the strangest part of all, all of the trailer wiring works fine when i test it. if i actually tow the trailer with the wiring plugged in, somewhere throughout the drive it gets blown. ideas?
    1 person likes this.
  2. Cableguy

    Cableguy Epic Member 5+ Years ROTM Winner 1000 Posts

    Are taking these measurements at the connector(On truck) with no trailer or are you taking measurements with trailer plugged in?

    Cuz I have a funny feeling its in the trailer side.
  3. Diceman

    Diceman Member

    im taking measurements on the truck side without the trailer plugged in.
  4. Cableguy

    Cableguy Epic Member 5+ Years ROTM Winner 1000 Posts

    Can you get at all the connections on truck side. If you could pull them down and inspect for damage or corrosion. Wiring is hard without being there to test it. Sounds like your ok with a multimeter. Do the same tests on trailer. Sorry I'm not much help. Sound like an intermitent short.
  5. 84fiero123

    84fiero123 Epic Member 5+ Years 1000 Posts Platinum Contributor

    My money is on the trailer wiring being bad.

    It is usually the problem in something like this.
  6. Diceman

    Diceman Member

    i just replaced the wiring in the truck and put dialectic grease on all the connections so it should be good to go for a while.

    the guys tested the trailer wiring and said it was kosher since my truck wiring didnt work when i picked it up. what would be the best method to check the trailer wiring?

    is is cool that the truck is popping out -11vdc as stated in the first post? im not sure how it would apply negative voltage.
  7. 84fiero123

    84fiero123 Epic Member 5+ Years 1000 Posts Platinum Contributor

    - any amount of voltage in a vehicle means one of two things. When you have that it means the red lead on your tester is on the ground.

    1, you have the leads plugged in the wrong holes in the tester itself, not the plug of the truck or trailer.

    2. You have a short some where in the wiring harness.
  8. Diceman

    Diceman Member

    the leads are in the correct holes, and i didnt move the ground from the ground spot the whole time. its possible that it is messed up, but messed up so that the ground is giving out positive voltage? i used one of those wiring harnesses so i havent hacked anything. not real sure how that could happen.
  9. Crawdaddy

    Crawdaddy All hail the Mad King!! Staff Member 5+ Years 1000 Posts Platinum Contributor

    something's definitley not right with your wiring in your truck if you're getting -11 volts, or any negative volts, when you're getting positive on everything else. There's got to be a cross or something in your wiring, something to do with the turn signals or running lights I would guess. However, that's VERY odd, especially since if a wire would be crossed to give negative voltage in that case, you should have burning wires or such that would cause fuses to blow or worse. I don't know what to tell you, my brain isn't working too good right now...
  10. imsubcrazy

    imsubcrazy New Member

    R U using a brake controller?

    Are you using a brake controller, or just going straight to the trailer? In some cases a straight connection might work, but I've never seen a setup on the large units I tow without an add-on brake controller. The trailer might be drawing more current than the fuses can provide directly. My brake controller is fused at 30amps.

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