Trailer Running Light Issue

[way0utwest1]

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.

[enblethen]

What I was getting at is they are different.
Could jumper functions at trailer, then verify terminals on truck receptacle are the same.

[JRscooby]

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]

You are aware that utility and horse trailers are not wired the same as RVs?
Wiring diagram

[Grit_dog]

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]

opnspaces wrote:

way0utwest1 wrote:

- brake lights work (Combination of Green and Yellow wires)
- both turn signals work (Green and Yellow wires)
- reverse lights work (Could be any color wire)
- running lights on side (top and bottom) of trailer work (Brown wire)
- trailer brakes work (Blue wire)
- rear running lights do not work. (This is what we all call your taillights and are powered by the Brown wire) Yet it appears the entire LED panel lights up for the brake lights. (Combination of Green and Yellow wires)

Your changes may be good, as far as it goes.

- brake lights work (Combination of Green and Yellow wires)plus a ground
- both turn signals work (Green and Yellow wires) plus a ground
- reverse lights work (Could be any color wire) plus a ground
- running lights on side (top and bottom) of trailer work (Brown wire) plus a ground
- trailer brakes work (Blue wire) plus a ground
- rear running lights do not work. (This is what we all call your taillights and are powered by the Brown wire) Yet it appears the entire LED panel lights up for the brake lights. (Combination of Green and Yellow wires)

The above colors really don't matter as they can change colors as they go around the trailer. But what I tried to did above is illustrate how each light is controlled by a different wire; Which is why some lights work and others don't.

[opnspaces]

You can basically ignore all lights except the two taillights that aren't working. They all run on separate wires and therefore do not affect one another. The exception is the ground and the running lights.

way0utwest1 wrote:

- brake lights work (Combination of Green and Yellow wires)
- both turn signals work (Green and Yellow wires)
- reverse lights work (Could be any color wire)
- running lights on side (top and bottom) of trailer work (Brown wire)
- trailer brakes work (Blue wire)
- rear running lights do not work. (This is what we all call your taillights and are powered by the Brown wire) Yet it appears the entire LED panel lights up for the brake lights. (Combination of Green and Yellow wires)

The above colors really don't matter as they can change colors as they go around the trailer. But what I tried to did above is illustrate how each light is controlled by a different wire; Which is why some lights work and others don't.

You should definitely check the grounding because it's the easiest thing to check. Pull a light off the back of the coach and find the ground. If there are three wires the ground should be labeled on the housing. If there are only two wires then the ground is through one of the mounting screws and you will see bare metal for the screw to touch.

But you're dealing with LED's and I don't think you have a grounding issue because if you did the brake lights would also not work. The running lights are usually wired with one wire that goes down the trailer and around the back. Each running light is T'd off that one wire. Somewhere in the back of the trailer the T-connection for the taillights is loose or disconnected.

Hopefully you can see the back of the taillights without removing them, But if not I would remove each taillight carefully being sure not to pull too hard on any of the wires. You need to be careful because if there is a loose connection you don't want to have the connection pull apart and drop the wire back into the trailer where you can't get to it.

With the running lights on, wiggle and pull the connections, squeeze them with a pliers. If the light suddenly comes on you found your bad connection. Unplug the trailer, cut out and redo the bad connection. If all the connections are good then you are going to have to find the other end of the T-connection. I would start up at the running lights across the top rear of the trailer. Pull each one carefully and check the connections. Sooner or later you will find the bad connection and repair it.

[CA_Traveler]

Also I'd expect that any horse trailer would have a battery and trailer brakes and that the circuit is connected to the frame. Others may have more experience.

And additional inside/outside horse related lights may share some wiring like a common ground.

I'm aware that some of my thoughts don't seem likely. However mfg companies will do what every is required to complete and sell a unit and one should expect the unexpected. They don't delay a build because of wire color or original parts availability etc.

[CA_Traveler]

I'd be interested in learning more about your LEDs and their "resistor". Neither your pic or link are visible.

After you get the lights working correctly the next easy step would be to measure the amp draw. Check the trailer draw, tow draw and both. It's possible that you are at the fuse/circuit limit.

Another area to check is the house battery and circuit. Possibly something is connected to that circuit. I'd hope there is a charge wire and a trailer brake wire.

And since it's also a camper I would expect the house battery to be grounded to the frame including the ground from the tow vehicle. I agree with others that a dedicated ground wire for the lights is best and you may/may not have that.

[JRscooby]

First thing I would do is get under and look at the routing of wires. If like many the marker wires branch off the taillight wire, that would be a connection to check.
All trailer lights should have a wire to carry the ground to at least frame of tow vehicle. Marker lights need 2 wires, and tail/turn should have 3 wires to fixtures (Note to OP. Most trailers built to be towed behind light vehicles don't have brake lights. When you brake works, that circuit is for the E brakes. To signal a stop, send power to both turn lights)
Most light manufacturers of light duty trailers still use the trailer frame for ground. They have a wire on the cord connected to frame, and wires from lights, or worse, depend on body contact to frame, as a ground path. IMHO, a much better plan is run the ground side just like the power side, and keep the frame above ground.

[way0utwest1]

Thanks, I'll take things apart Sat or Sun and look. All the lights appear to light up for braking, so perhaps a resistor lowers the voltage and light for the running lights/rear trailer lights.

I hear them called different things, but these are the lights that are always on when the truck headlights are on.

[BarabooBob]

From my 50 plus years of experience with trailer lights, troubleshooting should always begin with establishing a good, known ground from the light to the tow vehicle. When I wire up a trailer, all fixtures have a positive and a negative wire that goes to the tow vehicle. I don't rely on frame grounding.

[D_E_Bishop]

I'm a little dense and it has taken me a little while to decipher your post. I get the impression that what you are calling rear running lights are what we call tail lights. The thing that has me confused is the use of headlights and the clear lens on the light you show in your post.

It may be a little confusing but if those are red leds in that light, then I would bet that only part of the LEDs are lit, or, those resisters are used to allow them to work at a lower current flow and when you apply the brakes, either all the LEDs come on or full voltage is applied allowing them to signal you are applying the brakes.

And yes that can be done. Those resistors and diodes are there for a reason. I would remove and disconnect the lights in question and check for electrical operation of the wiring. If power is supplied when appropriate and the grounds are good, get new running lights. It doesn't seem to me that it is a ground issue and why did the trailer stop blowing fuses?

[enblethen]

Can you see a manuacturer's name on lights? I think I can see some information in lower portion.
Looks like there is some resistors in the light and some type of network!

[way0utwest1]

Here's the assembly: ***Link Removed***

This is original, on a 2015 Lakota Horse trailer/camper.

My first thought was resistor, but it could be capacitor or something else.