# Trailer lights help needed



## randyjaco (Dec 11, 2021)

The running lights on my trailer went out. All the trailer turn signals and the brake lights are working fine. None of the bulbs are blown. A while back, while connecting the trailer to my Tacoma truck, I got a spark while plugging it in. I couldn't find a blown fuse. So I don't know if the problem is with the truck or trailer. The truck lights seem to work fine, but they are not making the trailer lights function. Can someone please tell me which color wire make the circuit for the running lights?


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## Janderso (Dec 11, 2021)

I’ll be waiting for a smart fellow to help out.
The purpose of my post, in my experience 99.9% of the time the issue is with the trailer wiring.
Scotch locks and other poor connection methods are used in an application that is exposed to the weather causing corrosion, high resistance and other issues.


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## Bi11Hudson (Dec 11, 2021)

Most modern pickups have *separate circuits for the trailer plug*. Especially those that came from the factory with towing gear. My trailers all use a 6 wire connector, so I don't know which wire is for the running lights. As stated above, the problem probably lies with the trailer. But a blown fuse will be on the truck end. The WHITE wire is ground, of that I'm sure. Connecting a test light from that to the other three will quickly identify which is which. When testing, I usually set the 4 way flasher going, that helps isolate things quickly.

My most recent truck was a Chev DuraMax 3/4 ton. There was a relay panel, with fuses, immediately adjacent the truck fuse panel under the hood. A fuse for the trailer circuits is most likely under the hood rather than in the dash.

.


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## lordbeezer (Dec 11, 2021)

Most are brown and yellow


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## lordbeezer (Dec 11, 2021)

Test light should give the answer.


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## John O (Dec 11, 2021)

Standard here is
white-ground
brown-tail lights
green-right turn/brake
yellow-left turn/brake
I have seen many wired different but the majority are this way.


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## 682bear (Dec 11, 2021)

On a 4 wire plug, the brown wire is normally for the driving lights... I would assume that is true for a 5 wire plug, but I'm not sure.

I would guess, if it sparked as you were plugging it in, that the wire has a short to the trailer frame somewhere... check everywhere the wire comes in contact with the metal to check for cracked or worn insulation.

In my experience, the cheap harnesses last 3-4 years before becoming problematic... at which point they just need to be replaced.

-Bear


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## RandyWilson (Dec 11, 2021)

Year and model, please, so I can pull up a wiring diagram.


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## jocat54 (Dec 11, 2021)

I had the same thing happen on my 2014 Ram and it was a fuse under the hood by the main fuse panel-------had to order the replacement fuse no one carried it. Did southern engineer the fuse until the right one got here.


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## RandyWilson (Dec 11, 2021)

I'm heading to bed, so I picked a random example, '19 Taco 3.5L.   The trailer running lights have their own relay and 30A fuse in the relay box under the hood.


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## Eddyde (Dec 11, 2021)

I was having problems with lights working intermittently on my trailer. It uses the chassis/frame for ground, I noticed corrosion where the ground wires from the lights were attached to the frame. I cleaned the connections and it would work fine for a while but then the problem would resurface. I eventually got fed up and ran a dedicated ground wire. It has been working perfectly since.


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## gonzo (Dec 12, 2021)

Much data available on    E-TRAILER


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## Janderso (Dec 12, 2021)

RandyWilson said:


> I'm heading to bed, so I picked a random example, '19 Taco 3.5L.   The trailer running lights have their own relay and 30A fuse in the relay box under the hood.
> 
> View attachment 388202


I love this forum!


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## mmcmdl (Dec 12, 2021)

Great thread . I have a 7 blade type plug which fell out on my last trip to the mountains . It is now a three blade .  How hard can it be to rewire a new 7 blade plug onto the existing wiring ?


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## machPete99 (Dec 12, 2021)

Depending on whether the vehicle had trailer wiring built into the original harness, there could potentially be a controller box that someone added in, like this one:



			Amazon.com
		


If you follow the wires back you should be able to find it, and see if it is working correctly.
If the factory wiring is hosed and not fixable you could also splice in your own box.


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## matthewsx (Dec 12, 2021)

Hopefully it’s just a fuse but my experience is troubleshooting trailer wiring is almost always a ….shoot.

I buy wire by the spool and have a tester for the vehicle end.


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## Weldingrod1 (Dec 12, 2021)

+1 on using real ground wires... just bite the bullet and do it. You wont regret it!!

Sent from my SM-G892A using Tapatalk


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## davek181 (Dec 13, 2021)

Wire colors as mentioned earlier for the trailer plug
white-ground
brown-tail
green-right turn
yellow- left turn.

That is the standard recognized colors in the trailer industry, though many do what they please.

Colors from the car vary greatly.  

The biggest problem with trailer wiring is the car to trailer hookup.  Most american trailers use the 4 prong plug and the trailer is wired to have a taillight circuit and a left turn circuit and a right turn circuit.  Brake lights are achieved by lighting both turn signals.  Cars used to be wired that way too, till like the 70's or so.  The advent of imported cars changed that scheme by having a separate brake light signal independant of the turn signals, mainly to accomodate the amber turn signals.  This required a converter box to turn 4 wire cars into 3 wire trailer wiring.  That is excluding the ground which many people do anyway and rely on the trailer ball to ground the trailer body.  It works, but not a great idea.

Trailer converter boxes come in basically 2 varieties, powered or unpowered.  The unpowered ones use the cars wiring as their source power and light the trailer lights from that.  The powered units have their own power source and light the trailer lights using that and only employ the car wiring as a low amperage signal wire.  They are usually fused independent and will blow their fuse if something happens to the trailer, but the car circuitry will not be affected.

I imagine any manufacturer that has a tow package will have their own version of the powered converter for their own safety, as trailer wiring is totally unpredictable as a rule.  The car wiring diagram or owners manual should indicate which fuse(s) are for the trailer wiring.

A simple test light at the car end trailer plug will tell all.  You should get independant tail signal on one pin, left turn on another, right turn on the next,  Brake lights will light both turn signals if the car is wired through a converter. 

 99% of all trailer wiring issues are the trailer itself.  Fused power fed individually to the trailer plug pins will usually tell all too.  Lights will either not light or the fuse on the individual circuit will blow, and hopefully the idiot that wired the trailer followed the standard code for simplicity in diagnosis.


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## lordbeezer (Dec 13, 2021)

We’ve all seen trailer lights blinking while driving down road. That’s from trying to ground thru ball and coupler. I prefer to run a ground wire. Thought I posted this yesterday but didn’t hit the magic blue area.


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## randyjaco (Dec 13, 2021)

I found a blown fuse that I missed earlier. That didn't solve the problem either, but at least I know that the problem is not the truck. I got fed up trying to trace the issue on the trailer (the wiring is old), so I just purchased a new set of LED trailer lights. Hopefully, I will get them installed tomorrow. Thanks for all the help.


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## matthewsx (Dec 13, 2021)

randyjaco said:


> I found a blown fuse that I missed earlier. That didn't solve the problem either, but at least I know that the problem is not the truck. I got fed up trying to trace the issue on the trailer (the wiring is old), so I just purchased a new set of LED trailer lights. Hopefully, I will get them installed tomorrow. Thanks for all the help.


Change all the wire too, I’ve seen wire go bad in the middle and you wouldn’t know from looking at it.

John


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## randyjaco (Dec 14, 2021)

I had to change the wiring. The new lights had a similar but different wiring. No red on this one. I soldered all the connections and shrink-wrapped them. Hopefully these will last a little longer.


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## matthewsx (Dec 14, 2021)

It's already done but standard advice is to use crimps, not solder. Solder joints can suffer from work hardening and fail but you're not working on a yacht here (learned from ABYC Marine Electrical certification course).

JOhn


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## davek181 (Dec 14, 2021)

VW/Audi and other manufacturers are very specific about wire harness repair and they have a couple pages of how to properly crimp their connections.  They also specify no soldering in harness repair, nor do they use soldering in building the harnesses.  They do have some welded connections though that look like instantaneous spot welds with no heat damage to the wires.


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## John_Dennis (Dec 28, 2021)

An easy way to make absolutely waterproof connections is to apply a little hot glue to the splice or connection before the heat shrink tubing. premium Heat Shrink Tubing sometimes comes with glue already applied but you have to pay extra for that.


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