Trailer Wiring

Hello,

I have found the wiring diagrams (BELOW) for the trailer. Here is a guide to help you troubleshoot the problem.

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

If the fuse does not have power to it then it has to be a wiring issue because power comes from the battery to the fuse box. If surrounding fuses have power than the box itself is probably not at fault, although this does not eliminate that possibility completely. You will need to inspect the wiring going to the box and right under the box where they all connect. If the wiring is good then a swap of the fuse box with known good one will need to be made.

Please let us know if you need anything else to get the problem fixed. (BELOW)

Cheers, Ken

Electrical problem
2004 Chevy Silverado V8 Two Wheel Drive Automatic 103000 miles
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I am having problem with trailer lights. I have tried on 3 different trailers. So it isn't in the trailer. When I turn the left turn signal it works correctly. When I turn the right turn signal on both the right & left turn light blink. I have no left brake light.

I test the wires with a test light on the trailer plug (factory wired 7-pin) & it test the same way as above , so I am sure it is not a ground problem.

The lights on the back of pickup works correctly.

Thanks,
Randy

check the wires going to the trailer and make sure none have rubbed through. sounds like they are shorting out together. when they all blink are they dim. if they are, sounds like they would be shorting to that ground.

I check the wiring on the pickup & found nothing rubbed. If there were two wires shorting across I think that both the turn signal would flash when the right or left turn signal was turned on. Like I said when I turn the left signal on only the left signal blinks.

Thanks,
Randy

thats not true wiring can do some wierd things. Now when they are both blinking aare they both very bright, or is the one that is not suppose to be blinking dim.

The only time they both blink is when the right signal is turn on. The left one works correctly, but the left brake light does not work. Yes both lights are bright.

Thanks,
Randy

here is the wiring diagram for the trailer lights, there is a better diagram above in Kens post!!!!

I had the same problem on my 04 silverado. It ended up being the factory trailer plug. I bought a new one from the dealer and it fixed the problem. I first looked for corrosion but didn't find any.

Did you ever solve this problem? I have a very similar problem.

Yes, bought the female plug for the truck from the chevy dealer. When you have speperate stop and signal lights you need a converter to get it to work on a trailer with integral lights. There must be some diodes in the plug that we can't see. Good luck.

Actually, after much surfing today, I got an idea. I knew the trailer I was trying to hook up to had some poor wiring. When I hooked up the trailer to the truck, I blew all the fuses for the trailer side of the turn signals. Unfortunately, the fuses did not protect the flasher relay. The relay has contacts for the trailer and truck separately. I discovered the relay going to the trailer had fused. Managed to take the relay apart and pry the fused relay apart. Works fine now. Beats paying $97 at the dealer for a new one!

when the trailer is plugged into my son's truck everything works perfect, when plugged into the chevy and the left turn signal is on both the sides blink

SOUNDS LIKE A PROBLEM WITH THE CHEVY

USE A 12 VOLT TEST LIGHT--GROUND IT REAL WELL NEAR THE PIG TAIL

HERE'S WHAT YOU SHOULD GET

BROWN WIRE PIN---STEADY TEST LIGHT

GREEN WIRE PIN--RIGHT TURN --BLINKING TEST LIGHT (IF YOU TURN OFF THE TURN SIGNAL, APPLY BRAKES AND GET A STEADY TEST LIGHT)

YELLOW WIRE PIN--LEFT TURN--BLINKING TEST LIGHT (IF YOU TURN OFF THE TURN SIGNAL, APPLY BRAKES AND GET A STEADY TEST LIGHT)

WHITE WIRE--IS THE GROUND--IT NEEDS TO BE GROUNDED ON THE VEHICLE AND NOT DEPEND ON THE TOW BALL AS A GROUND FOR THE TRAILER

THINGS TO REMEMBER---THE TRAILER HAS 2 FILAMENTS IN THE BULBS, ONE WILL "BURN" (RUNNING LIGHTS) THE OTHER WILL BE REALLY BRIGHT (THIS WOULD BE THE TURN SIGNALS/ BRAKE LIGHT FILAMENT)

SO MANY PEOPLE WILL HOOK UP THEIR LIGHTS SO THAT THE RUNNING LIGHTS AND TURN/ BRAKES ARE REVERSED

THE TURN AND BRAKES ARE NOW DIM, AND THE RUNNING LIGHTS ARE BRIGHT - EVEN ONE SIDE OF THE TRAILER IS CORRECT AND THE OTHER SIDE IS WRONG

MUCH OF THE TIME YOU HAVE A GROUNDING PROBLEM, THIS MAKES CORRECTLY HOOKED UP LIGHTS "SEEK GROUND" WHEREVER IT CAN (THRU THE OTHER WIRE) LIGHTS MAY BLINK DIM, EVEN BOTH FILAMENTS WILL BLINK)

I HAVE MADE SEVERAL REALLY LONG ALLIGATOR CLIP JUMPER WIRES

WHEN I TEST,I GROUND TO THE BATTERY NEGATIVE POST (A GROUND DON'T GET NO BETTER'N THAT!

I REMOVE THE LENSES AND CONNECT (OR TOUCH) MY JUMPER TO THE PLATE INSIDE THE LIGHT FIXTURE. IF THIS WORKS WELL, EITHER MY LIGHT'S GROUND IS RUSTY, OR THE GROUND FROM THE TOW VEHICLE IS BAD

REMOVE THE BULBS, LOOK INTO THE BOTTOM OF THE SOCKETS, IS THE CONNECTION THERE? IS IT MELTED? HAS ONE OF THE PINS SUCKED BACK UP INSIDE THE SPRING LOADED BOTTOM?

HAS SOMEONE INSTALLED INCORRECT BULBS? LAST ONE I DEALT WITH, SOMEONE INSTALLED, RATHER "CRAMMED" "1156" (SINGLE FILAMENT) BULBS IN INSTEAD OF "1157" DUAL FILAMENT BULBS

SENDING A PIC OF MY TEST LIGHT IN ACTION (ANOTHER KINDA USE FOR IT) A VOLT METER WILL WORK IF YOU HAVE ONE

KEEP US POSTED ON PROGRESS

THE MEDIC

Electrical problem
2001 Chevy Silverado V8 Four Wheel Drive Automatic 64233 miles

the trailer connector on the truck came from the factory. i tested the continuity on plug ok.the brown wire that says on outside cover says running light the shop manual ligthing system 8-321 shows it going to a trailer park inline fuse.all the fuses in the fuse box are ok. the brown wire has always been dead. is there a inline fuse and where or how can i fix it without giving GM a blank check to fix it

That brown wire is only "hot" with the park lamp relay enegized. Top picture is light duty hitch, bottom is heavy duty.

thank you well done.... it looked like there was a in line fuse looking under truck....thank you again

Your welcome!

Electrical problem
2003 Chevy Silverado V8 Four Wheel Drive Automatic 140000 miles

the truck has a factory installed tow package the wireing is in very good condition.
when the left turn signal is turned on the trailer four way flashers go on for the trailer when the brakes are used only the left brake light on the trailer works all other lights work as they should right turn signal flashers and running lights work correctly i have checked on other trailers and the problem is the same so it is not the trailer lights i have tried different plug in units with same results

Identify the left and right signal power supply on the truck. Turn the left signal on and let me know if you are getting power from both the left and right power supply wires.

I had a brake connector wired into the bed for a 5th wheel. When I bought the truck the factory 7-pin on the bumper was corroded so I bought a new one. When the shop wired the connectors now when I press on the brakes my left marker lights come on but the brake controller isn't sending power to my trailer brakes. I'm not sure which wire is ran wrong?

see pic red is hot wire and make sure you have a good ground. yellow is lh t/s and dk green rh t/s brown is tailights

The diagram says W/O crew cab. Mine is a crew cab. Does it make a difference? Thanks

is it a 2500 or 3500 you didn't say. besides that is only the ground that they are talking about not the connector

Sorry, it's a 2500hd Duramax. Thanks

Electrical problem
1999 Chevy Silverado V8 Two Wheel Drive Automatic 216490 miles

I hook my trailer up to my truck and plug in the lights. I check the lights to make sure they work,check the blinkers,brake lights and tail lights and they all work correctly. Here is where the problem starts, when I hit my brakes or turn my lights on and hit my blinkers, the lights on my trailer flash like lights at a rail road crossing.

First, I have to tell you, I laughed when I read your description. The RR crossing lights got to me.

Explaine this... do they flash left, right, left... or do they all seem to go haywire? Also, you mentioned first you checked them and they all work. Do you have to turn the key on or something for this to happen or does it do it all the time? Finally, are you sure the wiring on the trailer is good? Have you checked the plug on the truck to make sure everything is working properly using a test light? To be honest, it sounds like either you have a bad trailer ground or mice may have gotten into the wiring.

Let me know.
Joe

Yes,this happens when the key is turned on. When doing a basic check of the lights, the left blinker works,the right blinker works and the brake lights work, it is only when I turn on the lights or hit the brake and then check the blinkers that they flash left,right left,right. I completely traced the wires on the trailer and all is well. I checked the plug on the truck and it checks out as well. I'm about ready to pull my hair out.

Don't pull your hair out. I know it is frustrating. Have you tried running a seperate ground wire from the trailer to the battery itself in the truck? I still think it is a ground problem.

O.K. So before I run a seperate ground I take another look at my wireing harness just to make sure everything checks out, when my wife yells at me telling me that they just started working. So my guess would be in the harness some where. Now my nest question is when I jiggled the wireing harness and the lights started working why would my plug so to be working properly before I Jiggled the harness. I hope you understand the question.

I wish I could meet you. You sound just like me and my wife. (LOL)

If that is the case, either you have a short in the wiring itself, or there is a ground that is now making a better connection.

I know if sounds crazy, but a weak ground will do strange things. I have an old Hi Lo that I refuse to pull any more. The last time I worked on it, when I put on the brakes, the lights inside the camper would turn on. Believe it or not, it was a bad ground that caused me to loose more hair than I had to loose. That is why I am pushing you in that direction.

Check it out and let me know if it helps.

Joe

I checked the ground,and it looked good but to make sure I disconnected it sanded the area on the frame to make sure of a good ground and re grounded it. Every thing is still working, so it has to be in the wireing harness somewhere I would think. P.S. Just like you said.

They are a pain. Chances are there is a wire that has the insulation worn through and is shorting. Last year I went nuts with mine. Like I said, when I hit the brakes, the lights inside the trailer turned on. You should have seen that at night. It was like someone was living in there as I drove them around.

Randy,

I have the exact same problem with the right turn signal on my trailers. I have 2 trailers and they both do the same thing. In addition hooked up a differnt truck and the lights worked fine. Got ripped off by a trailer place in Salinas, CA ($190.00) bucks worth of BS Left turn blinks just find. Right turn blinks emergency on the trailer but right turn on the truck. Replaced the truck plug in with a new one. Did you ever figure out what was causing your problem. Z....

check ground from trailer to truck

Electrical problem
2005 Chevy Silverado V8 Four Wheel Drive Automatic 37700 miles
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I keep blowing my trailer fuse when I connect my seven plug connector from my small horse trailer to the truck. I have checked all the lights and grounding on the trailer. The lights work fine off a battery, however, when I connect the trailer cable with the truck running, the fuse will blow. If I connect with the truck off, it will work for 5 minutes and then blow. I'm not sure if I can increase the fuse size or not. I have a utility trailer with a four plug connector that works fine. The hitch is a GM hitch with the prewired cabling.

Electrical problem
2003 Chevy Silverado V8 Two Wheel Drive Automatic 154000 miles
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Does the 2003 Silverado have a snap in trailer light harness or do I have to splice into the taillight wiring?

What about trailer brake wiring?

you should be able to purchase a quick connect trailer harness kit for it.

sounds like the problem is with the trailer. Make sure all of your connections in the trailer wiring are good clean connections.

ok

As I wrote, I had a new plu put on the trailer and the problem is still occurring with two differnt trailers ... but when I hooked up a differnt truck everything was ok ... so now I just have to find the ground. I always heard that 90% of electrical problems are bad gounds.

I have a 2004.5 Chevy Silverado crew cab 4x4 with the duramax diesel and the alison trans with 29,995 miles on it. I just started having problems with the factory trailer wiring circut. When I step on the brakes I only get the right brake, and when I turn on the right blinker, I get power to both right and left blinker. This test was done with the trailer hooked up and also without being hooked up using a test light. This problem is at the rear on the factory 7 wire plug and at the fithwheel wire assimbly between the cab and the bed.

Any ideas ? chevy said maybe a bad relay under the hood but which one? it's not marked for trailer on any of the relays under hood, only fuses which are all good. This truck does not go off road and is very clean.

Thanks ,
Corby