Forum Discussion

way0utwest1's avatar
way0utwest1
Explorer
Aug 02, 2019

Trailer Running Light Issue

I have a 5th wheel horse trailer with some kind of light/wiring issue and I'm hoping someone can help me debug this.

On an earlier trip, we didn't have the rear running lights showing on the back of the trailer. A friendly officer gave us a warning, and we bought some LED headlamps from WalMart, duct taped them on, and got home.

We discovered a blown fuse, which made sense. We replaced it, and went on another trip a month later, again, finding the rear running lights not working. Fuse blown, so replaced.

We thought we had truck wiring issues, so we took to a mechanic with our other horse trailer (not camper). They didn't find any issues, and we used that trailer for a few months every week without issues.

Fast forward to last week. We think the 5th wheel camper has the issue because the truck works with the other trailer. We were worried about some corrosion in the plug, so we rewired that with a new plug. Tested it out and find this:
- brake lights work
- both turn signals work
- reverse lights work
- running lights on side (top and bottom) of trailer work
- trailer brakes work
- rear running lights do not work. Yet it appears the entire LED panel lights up for the brake lights.

I'm not sure where to go, and I'd prefer not to pay someone $$$$ to go searching around. Any ideas out there are appreciated.
Seeking Advice
  • Grit_dog's avatar
    Grit_dog
    Navigator
    Aug 04, 2019
    Didn’t read the whole thread but you’ve narrowed down the problem already to the rear lights themselves or the running light wires to the rear lights only.
    Take lights out unplug them test for 12v at plug. If yes lights are bad.
    If no, wiring is shorted/grounded out and likely past the wires that split to the other running lights.
    Too much load, not an issue for you, or a live short pops fuses, so likely have a wire to the rear lights shorting out on the trailer frame somewhere.
  • JRscooby's avatar
    JRscooby
    Explorer II
    Aug 04, 2019
    enblethen wrote:
    You are aware that utility and horse trailers are not wired the same as RVs?
    Wiring diagram


    If you look, the pins on 7-blade connectors do the same job RV, horse or utility. Otherwise would need to rewire every time you changed trailers. Colors my vary, so never should be depended on.
    Now if you get into trailers designed to be pulled by CMV, the pattern changes, (no E brake, but brake lights, tail and marker separate) but the design of outlet and plug are made so they can't be interchanged.
  • enblethen's avatar
    enblethen
    Nomad
    Aug 04, 2019
    What I was getting at is they are different.
    Could jumper functions at trailer, then verify terminals on truck receptacle are the same.

About RV Tips & Tricks

Looking for advice before your next adventure? Look no further.25,102 PostsLatest Activity: Jan 18, 2025