Trailer tow wiring

Mitchell Gay · February 14, 2020

Has anyone had problems connecting a trailer and trailer lights not working? I was told by a Chevy tec that the 2020 trucks will only operate LED lights on trailers.

redwngr · February 14, 2020

I'd bet the tech was incorrect.

I can't imagine that they would do something that forces potential customers to redo trailer lights.....

I frequent several GM truck forums, with lots and lots of towing reports for the 19/20 1500's and the '20 HD's and have never heard that one.

7 pin plugs (especially those used infrequently) are notorious for collecting contaminant and/or corrosion and requiring maintenance to ensure good connections. If wondered if there are more than one 'standard' that they are built to, resulting in pin/socket connections that are loose enough to make this more difficult.

But that's been an issue for many years. (at least with the trucks / trailers that I've run)

Edited February 14, 2020 by redwngr

Vasa1 · February 15, 2020

18 hours ago, Mitchell Gay said:

Has anyone had problems connecting a trailer and trailer lights not working? I was told by a Chevy tec that the 2020 trucks will only operate LED lights on trailers.

That’s funny! LED or regular lights, 12v!

yousaveone · February 17, 2020

You need this 19366958 .

I have the tech - trailer package therefore no flat 4 connector. With this $14 adapter my truck recognizes my flat four trailer. On shop chevy parts it states that this adapter has resistors in it to compensate for the voltage draw that the truck monitors. Either way it works.

Mike Geringer · February 18, 2020

Yes I have had this problem Still do. 2 diff trailers both work perfect on a 2008 gmc, 2015 chevy and a 2018 gmc no bulbs out. plug them into my 2019 gmc and no trailer running lights. tells me bulb out. brake and turn signals work perfect. dealer can not find answers. Hook up to brand new trailers and it works perfect. If I disconnect one side or the other side lights it works perfect. I'm guessing the allowable range they programed the computer for is too narrow for older conventional trailers. Tried replacing plugs and lights with all new, no luck. This spring I will run a separate ground wire to each light instead of allowing chassis ground for the lights. Maybe the resistance is just to high on an old trailer.

Larry Belford · February 19, 2020

I have the same issue going with my 2020 Trail Boss. Tried a trailer and no lights, tried a lighted hitch cover and nothing. They tried tell me that the items do not pull enough power. As a trouble shooting step I asked them to take my pig tailed wiring harness that allows me to have a the 7 pin connected to the bumper while giving me a 4 pin flat connector to another 2020 truck. They did and it worked perfectly. However, my truck has the "upgraded" tow package that includes the camera views and everything. The 2020 truck that it was tested on where it worked perfectly had the tow package one step below mine. So, in short the package that has a 4 pin built into the bumper of the truck as part of the 7 pin connector, your accessories and older trailer will work. If you have that same truck with all the camera views and the top two bumper mount connections in your left of the plate bumper mount are camera connectors and not the 4 pin, you will have the problem of the lights on an old trailer with 4 pin not working and neither will accessories that are powered by that 4 pin. The high end tow package has issues. The techs were able to get it working when you first turn the truck on, but as soon as you press the break is pressed the connections stop working until you turn the truck off and back on. There is a sequence somewhere in the line that probably needs a dummy load or some type or a different type of power draw regulator. This is hopefully going to be in a software flash or factory recall, SOON I hope.

Rsktm300xcw · February 20, 2020

Lots of posts on this. Go back through older posts. There is a trailer light control module reprogram that will probably help. Just look back through older posts.

goosehunter · February 20, 2020

One of my trailers is led and other(cargo) reg lights, the regular lights take a few seconds for the trucks computer to recognize.But they do work..

GH

Larry Belford · February 29, 2020

After weeks of searching and a couple hundred bucks, I have finally found something that works. The harness is built to power accessory lights and even tow hitch covers. I have had no problems with anything on the tow end since putting the harness in. It took 10 minutes at the most. It is made for the light bar but gives you an 4 pin flat that can be used as well. I hope this helps y'all like it did me.

https://www.amazon.com/529005-Connect-Harness-Silverado-Sierra/dp/B07V82RZNT

Ancient Man · September 28, 2020

Mitchell,

You may have found a solution to your problem, but allow me to share what little I have learned: I have a 2019 Siverado LTZ. Like you, I had a trailer light problem. Actually, I have several problems. I have a utility trailer which has all LED lights. My truck tells me that it is disconnected, if it even is hooked up and the lights occasionally work (They all work when I'm pulling it with my wife's Ford Escape, ALL THE TIME). With my flatbed (with brakes), the truck says it is disconnected, but all lights work (incandescent). My boat trailer has many lights and the truck and lights work as they should. Haven't tried my car dolly, but assume it will not work because it has few lights and all are LED.

First, went to my dealer, telling them about my trailer and how the lights worked with my wife's car. They replaced the module, with the tech saying he hadn't had to replace one before, but lights on utility trailer were working. I pulled the trailer two hours from home and was miserable for the entire 4 hour round trip. I kept getting error messages on both my info screen and the console in front of me. Driving on the Interstate, it is a wonder that I wasn't killed while being distracted, trying to dismiss the messages.

I found a forum online and there seem to be several solutions, all which will cost ME money.

I went back to the dealer and the tech came out and explained the issue. According to him, the trailer must pull at least 55 milliamps before the module will acknowledge the presence of the trailer. My utility trailer, with all LED lights, only pulls 40 milliamps, hence my problem. He thinks that if I can add a resistor to my white ground wire, my problem will disappear.

I told him to PLEASE tell Chevrolet that it shouldn't be my problem, because it is their problem. Remember the old days when we hooked up our trailers and the lights actually worked?? If enough of us scream loud enough, maybe they will come up with a solution. It is their engineering which created this issue. THEY should fix it!

In the meantime, I think I will try adding incandescent bulbs to my utility trailer to up the draw. Of course, I will have to have my lights on, all the time, for this plan to work. We'll see.....

Virgil Lee · August 21, 2021

I have a 2020 Silverado 3500 LTZ with the trailer towing package, non of my boat or landscape (4 flat wire connector pin) trailers will operate correctly. GM needs to get out a bulletin on this and let dealers know the problem. The turn signals and brake lights work, but the running lights will not work on any of these trailers. I used the same 7 pin to 4 wire pin adapter that I had with my 2015 2500 Silverado. I get warning messages that say the trailer is disconnecting while driving. I have replaced the adapter twice, with the same results. Additional, with the truck off and those trailers plugged in, I get both lights on the trailer flash on momentarily about every 5 seconds.

I called the nearest dealer and they do not have a clue, they said to make an appointment, and leave the vehicle so a technician can troubleshoot it? I called a 2nd GM dealer in a more rural area, and he said that he had several customers with the same problem, and the adapters will not work with these new trucks, GM is trying to say that those trailers are not compatible with their harness. WTF? The problem is with the new technology, not the trailers that work with any other truck. The inteli-trailer and adding 2 camera ports instead of a 4 wire flat pin connector created this problem. Pease call your Customer service VP and let your voices be heard, It's ridiculous that after spending 70k plus on a truck that the trailer running lights do no work. The rural Chevy dealer, said they solved the problem, by connecting or splicing into the rear tail lights the old fashion way and connecting a new 4 wire pin.

SoxFan904 · June 16, 2025

Hello everyone, I know this may be a long shot and is very specific to my truck and RV, but I wanted to see if anyone else out there experienced the same thing I am and can provide any suggestions or insight.

I currently have a 2020 Chevy Silverado 1500 LT Trail Boss. It has a factory tow package with the factory break controller. Scanning the QR code on the driver’s side, it came with the IOS Infotainment system (no built in nav, just Maps+). After months of research, I updated to the IOU (advanced trailering app, navigation and wireless CarPlay) version of the Infotainment radio module from Infotainment.com

The IOS version had a trailering “app” on the screen that would only allow a light check and would activate when my trailer was plugged into the 7-way connection with my headlights on. Additionally, the break controller would also indicate the trailer breaks were active. Since the install of the IOU unit, when I plug in my trailer, the lights work as intended, as well as the trailer break controller also indicates a trailer is connected, however, the trailering app in the Infotainment screen does not “register” a trailer connected.

When troubleshooting, Infotainment suggested to disconnect the battery for 20 min, then connect, lock the door, turn on the car and reconnect, this did not work. Additionally, I read that plugging in the 7-way while the car was off fixed this issue for some folks, that also did not work. I also read information about Chevy changing the “power output” from the 7-way connectors in 2020 and newer models, and that caused a problem with some trailers. I purchased a Curt 57003 LED-Compatible RV Blade Vehicle-Side Trailer Wiring Adapter, which was recommended to “signal” the Infotainment system a trailer is connected, especially for computers that have LED lights (which mine does). This is also supposed to solve the problem of the 7-way harness in a custom “control box” as my trailer is a Keystone Cougar 30BHS with a Giggy box, where the 7-way harness is connected to.

I apologize for the lengthy post, but I am baffled as to why this isn’t working. I pasted some links to different articles and information below. I also am going to look into the GM trailer simulator (listed below) and also see if any friends have a trailer I can plug into the 7-way or 4-way to “test” and see if its my camper or my truck causing the issue.

Any insight or suggestions are much appreciated, and thank you in advance.

Links:

Curt 57003: https://www.amazon.com/dp/B00AFVOF3M?ref=ppx_yo2ov_dt_b_fed_asin_title

IOU Infotainment Upgrade:

https://infotainment.com/shop/interior-accessories/infotainment-radio-upgrades/2019-2022-chevrolet-silverado-mylink-iou-gps-navigation-radio-upgrade/

GM Trailer Presence Simulator (I am considering purchasing, but it is very expensive):

https://techlink.mynetworkcontent.com/wp-content/uploads/2019/02/GM18-460.pdf

https://static.nhtsa.gov/odi/tsbs/2024/MC-10249034-0001.pdf

https://static.nhtsa.gov/odi/tsbs/2022/MC-10213515-0001.pdf