"Check trailer wiring" warning on my truck display

[Dan Davis]

Hello,

I towed first time over the Memorial Day weekend with my new truck and fifth wheel:
2024 GMC Sierra 2500HD
2023 Jayco Eagle 321RSTS

Every once in a while I received warning on my truck with message of "Check trailer wiring". Then it said that brakes are connected. I stopped multiple times to check: unplug/re-plug and check lights. everything was working.

Does anyone have an idea how to investigate this issue?

Thank you very much for your help, regards, Attila

I have the same problem for two months now: check trailer wiring, trailer brakes connected, ( then) Service Trailer Brake System. I just negotiated 175 miles with no trailer brakes as they dropped out completely. The truck is a 2500 HD Duramax Chevy. The Jayco Dealer will be dismantling for the third time. This time all wiring from front, remove all wheels, check all magnets, etc. Two seperate grounds fell out of different wire nuts in front frame junction box. This is fourth major wiring issue found. Photos to prove it. The truck was wired by totally untrained, unqualified labor. There is know way this vehicle should have left the line. Could not have passed the PDI inspection…. First night in this trailer, the furnace quit and so did the fridge. The fuse under the fridge blew. I removed the negative battery cable, then when loosening the bolt on the positive side the cable fell out of the connector ( it was crimped on by a thread). The list goes on and on. Chevys are sensitive: but the truck is not the culprit.

 

[Dan Davis]

My trailer is 32’, a 2023 Jayco 26FK. Delivered in May. I received my truck in June, both brand new.

 

[Kim Gass]

We had this happen driving across Labrador
it takes but s speck of croosion or a tiny piece of dirt in the receptacle to foul up the connection
A magnifying glass and dielectric goop works wonders

 

[Dan Davis]

Hopefully you got it fixed. I'm having the same issue now; constant "Check Trailer Wiring" messages where lights work but not the brakes.
Trusted RV Mechanic found a loose ground wire on the RV side of the wiring harness. So I had brakes until I drove home and parked the trailer, went to hook it up 3 days later and instantly got the CTW message again.
Trusted RV Mechanic will be looking at the trailer two days from now. Based on web research, it may be that the solar panel is overfeeding the battery and making the GM app think it's not working right. The plan is to remove solar from the electric wiring and check again.
The Mechanic's hours are going to be at my expense unless he finds some blatant violation of electrical code or common sense on Coachmen's end.
More later.

Interesting: my two solar panels are from the manufacturer. There seems to be enough on this specific concern that they should have something from GM in particular if it were their issue.

 

[jhershon]

Have same issue. Did you get any resolution? How did GMC handle it?

 

[David_ski]

I have often got that message on my F250. It has happened on both my boat trailer and my 5th wheel. I checked the wiring on the truck and trailers, and everything was just fine. I added some dielectric grease to the trailer plug, and my trailer wiring messages have disappeared.

 

[Jeff4310]

I found the problem, I installed an in the bed 7 way connector, at the y connector at the bumper it was not locked in all the way, I lost right rear turn and when I plugged my trailer test plug, it showed no right turn followed back and found obvious movement, latched and tied.500 miles and no more problem. ������

 

[Dan Davis]

Trailer Wiring Issues

The GMC dealer listened to me in detail and did replace the 7 prong adapter. It is a better fit for my 7 way plug. Noticed this immediately. However, the biggest issue was a set of sliced trailer brake wires, found at the rear axles, which, once repaired, finally put an end to the trailer messages. We had over 8 legitimate wiring issues that were a direct result of amateurish production/ manufacturer errors. Improper crimping of cables, improper installation of wire caps, loss of grounds X 2, blown fuses, poor bulkhead connections, wiring too short to meet terminal ends and subsequent sliced wiring. I have photos to back up my statements. Good luck with your trailer!

 

[Dan Davis]

Question!

I found the problem, I installed an in the bed 7 way connector, at the y connector at the bumper it was not locked in all the way, I lost right rear turn and when I plugged my trailer test plug, it showed no right turn followed back and found obvious movement, latched and tied.500 miles and no more problem. ������

Hey, I wanted to make sure you got my first reply. I wasn’t sure Jayco would allow? Also, this afternoon I just returned from a 4 hr destination: trailer brake message came on regularly within two miles of my dealer! I pulled in, had them check the 7 way plug. That forward 7 way harness is going to have to be replaced. Wow. ‘23 Jayco WhiteHawk. Used only three times since purchase in May 2023.

 

[Edutron]

Started to occur occasional on 2020 GMC 3500 Dually Denali. My fix was to spray the 7 pin connector with electrical contact cleaner. FIXED

 

[Dan Davis]

Wiring Saga Continues

One more trip with about 3.5 hrs one-way then on the return the trailer brakes went out first intermittently then off and on constantly. Trailer is back at the dealer. They are going to replace the forward seven-way harness in another attempt to find something obvious. A shame that Jayco won’t lend assistance. Without wasting all of my time, I know they’ll just tell you to go to “Your Dealer”. Every wire on that trailer will have to be inspected first then checked with a voltmeter, etc. in my opinion the underbelly should be dropped and the brake wiring restrung. I’ve dried out the trailer connector per your mention and it has always looked brand new. So,

 

[redenbacher]

Before my FW, I had a Jayco White Hawk TT and a GMC truck. GMC blamed Jayco and Jayco dealer blamed GMC. Dealt with that issue for 7 years. Even bought a different GMC truck thinking that would fix it. I learned in my case it was a Jayco brake issue. Never solved it. One thing I learned was the longer I drove the truck trailer combo, the more frequent it would happen. Fortunately, I live in the flat part of the US so was able to deal with it by keeping long distances behind others. Changing the cord and 7-pin (both sides) never fixed it. In my case I don't think it was a short, rather I think it was a resistance problem--the longer I drove, the more consecutive days of driving--the worse it got.

 

[Dan Davis]

Check Trailer Wiring continued

Just found out that on the 2024 HD Chevys, when towing your trailer if equipped with solar panels: if the solar panels charge the trailer battery voltage above the vehicle’s available voltage to the trailer…. The higher trailer battery voltage will back feed into the trucks electronic trailer brake control module and will shut down the trailer brakes. So, throughout all of these episodes we found several wiring issues with the trailer chassis: however, the constant check trailer brakes and subsequent dropping out o the trailer brakes; loss of function of trailer brake controller; is a GM problem. There is an available GM Bulletin which now has an available part# for replacing the electric trailer brake module. Now this failure affects a lot more vehicles but was originally for the 2024 HD’s only. Good Luck!

 

[ARoamer]

Light duty service bulletins, the HD models are not in these-
https://static.nhtsa.gov/odi/tsbs/2023/MC-10231817-0001.pdf

https://static.nhtsa.gov/odi/tsbs/2023/MC-10236167-9999.pdf

Service bulletin specific to 2024 model year-

service bulletin #23-NA-113 that may identify the issue specifically on 2024 2500s/3500s. The service bulletin states the trailer solar panels may charge the trailer batteries to a level higher than the truck battery and cause it to backfeed to the truck which places the trailer brake module into a “safe mode”.

 

[Sheila2024]

I spray both male and female connections with silicone spray. It lubes the connection and does not draw dirt like grease.

They had the same issue on our 2022 GMC Sierra We have a 2024 5th wheel North point camper we had a sensor replace on the truck and the plug for the truck so nothing changed
Now have purchase a 2025 GMC AT4 and we are having the same issue. We have contacted Jayco and GM and of course they are blaming each other still. This started just as a year ago when. We had an Eagle 2022 it did the same thing on our 2022 also but not as much. Now this new truck the brakes pretty much don't work much at all on the trailer. It sounds like it's a GM problem. When we brought our camper to the dealership 2 different times they couldn't find anything wrong. I don't know what else to do. All I know is it's very unsafe. Hope we stay safe traveling. When you have a brand new camper we'll a 2024 we are not going to leave it sit there and not use it because there's a problem with GM or Jayco but no one wants to fess up.

 

[Sheila2024]

So what do I do when Jayco says it's not them? I'm sure it is as we have towed a horse trailer, dump cart and a car trailer and no issue l. When we had the trailer in last fall they hooked the trailer up to a dodge or a Ford and said they had no problems. We are on our way camping my husband stopped and plug the plug now into the bump outlet instead of the box and seems to have some breaks off n on.

 

[Grumpy]

When you have a brand new camper we'll a 2024 we are not going to leave it sit there and not use it because there's a problem with GM or Jayco but no one wants to fess up.

Do you have solar panels? Did you read the above(post 34) regarding the service bulletin for GM?

 

[Travln2]

I had 2 out of 4 brakes with wires dangling inside the drum, wearing off the insulation. I imagine that's a fairly common issue.

 

[JFlightRisk]

I've poked around forums for the "Check trailer wiring" issue on GM trucks, and there were a ton of thoughts on why it's happening. All over the spectrum. They range from a brake wire shorting to ground, the brake controller itself, RV battery voltage either too high from the generator being on or solar charging, or too low from the inverter draining the battery faster than the truck can recharge it, LED trailer lights not having enough resistance, and even the 7-pin plug needing the double brass contacts for each circuit instead of just a single contact point on it. There are You Tube videos out there on the subject too. I agree to have the dealer check for TSBs on the subject.

 

[ClarkeNorman]

Hello,

I towed first time over the Memorial Day weekend with my new truck and fifth wheel:
2024 GMC Sierra 2500HD
2023 Jayco Eagle 321RSTS

Every once in a while I received warning on my truck with message of "Check trailer wiring". Then it said that brakes are connected. I stopped multiple times to check: unplug/re-plug and check lights. everything was working.

Does anyone have an idea how to investigate this issue?

Thank you very much for your help, regards, Attila

We've had the same problem with our new 2025 Pinnacle. Turns out that the plug on the trailer needed to have the two blades in each of the seven wires pushed together slightly. I used a small flat screwdriver to do this. The problem is that if the two blades aren't close enough together then they won't make a good connection when the plug is inserted into the truck connector. The truck connector has one blade per wire and it slides between the two on the trailer plug. You need to have some pressure being applied by the two blades to ensure a good lasting connection. Loose blades will make intermittent disconnects as you bounce down the road.

Safe Travels!