Trailer lights

Major Tom · August 29, 2021

I was having nearly the same problem with a new fifth wheel. Works great with my bumper bull flat bed trailer, all LED lights. About half the times I plugged in the fifth wheel, all LED lights, I would get the trailer not connected message. I just had to push the trailer plug in a bit further! You may also try cleaning the connections. Bed and bumper connections are in there factory postitions.

Hope this helps.

Virgil Lee · October 13, 2021

Hey Jordan, I am having similar problems with my 2020 3500 HD.

Since I upgraded my 2015 2500 Silverado, I do not have any running or tail lights on 4 of the 5 trailers that I own. It seems the advanced trailer system used in the 2019 thru 2021, with integrated trailer towing was released before being fully vetted. I have purchased 3 of the 7 wire to 4 wire adaptors, including one from GM and all have the same results, the brake lights and turn signals work on the 4 wire flat trailers, but no daytime or running lights, which makes trip to the early morning boat launch unsafe and illegal. They have replaced the 4 wire plug on this new harness with 2 individual port plug-ins for all those folks out there, who need to plug in their front and rear cameras on their campers, again WTH? Thus far, all I can get from Chevy is that their trailer system is working fine and my 4 trailers are not compatible with their advanced trailer wiring system; can I please have my dumber system back, that actually worked?? WTH, the 4 trailers worked on my 2015 2500 Silverado and continue to work properly on my wife's 2019 GM SUV. It's ridiculous that GM has not addressed the problem and is blaming our trailers, I would expect more after the purchase of a $75k vehicle. Another annoying feature of the advanced system is a quick flash (pulse) of the trailer and truck rear lights about every 5 to 6 seconds when the lights are plugged into the truck and the truck is turned off. It appears that the advanced trailering system is looking for a resistive load that most the 4 wire trailers do not have. Note: to add further insult, my buddy was over with his 2021 Ram diesel and the lights work fine on his truck! Everyone having this problem, please contact GM, get a case number and do not accept their corndog excuses, don't they realize we vote with our dollars. I will trade my beloved Duramax for a Cummings or Powerstroke, if I can tow safely tow after dark!!

kmonto · October 24, 2021

Rough trip back from Aransas, Tx this weekend. 2020 2500hd diesel towing a 28' open range TT. I have 29k miles on it now. Took truck and camper a few months back to Colorado and had zero problems with trailer and hookups. On the way down and real close to my arrival location, right trailer light turn signal went out on this 2019 TT. So it would have appeared, but found out later that was false by the truck. Before my departure, I used cleaner and electronic grease on the connector on the TT. On way back from Aransas to Arkansas, truck kept stating trailer was attached and then not attached. Left, then Right turn signals, then no brakes on trailer numerous and infrequent times (great when you just don't know if you will have the same stopping distance that you had only moments before). Got online and found the #84 fuse was the electronic brakes was blown. Bought a replacement and it worked for 10 minutes then same problem again. Had to drive without trailer brakes for a while. Took it to RV shop ($190 bucks), had them test the trailer and replaced the main plug cable to the junction box, put a fuse in #84, worked for 10 more minutes then stopped at a GMC dealership. 2.5 hours later - they replaced the fuse and stated they have no idea what is wrong with it. Said, after my 180 dollar diagnostic bill that they can't figure it out and would requirement more time maybe a week, best of luck on your journey home. Brakes went in and out the rest of the way but the trailer lights worked. Fuse is blown again.

Not going to lie, I wasn't a chevy guy for years due to poor quality. I took the jump on this 2020 and I can tell you that I am having a hard time with this. My 10 year old ford f150 NEVER had any of this type of problems. It did have a transmission module that went out but they quickly fixed it.

Maybe with 5+ pages on this forum alone, maybe a class action lawsuit is in order. Just imagine if someone is towing and ends up rear ending someone due to the brakes on the trailer just randomly disconnecting while braking and then randomly reconnects.

I am out 320+ bucks on this and no answer is in site. My local dealership in Conway, AR (Chevrolet - haven't tried the GMC one yet) has clueless individuals working there.

kmonto · April 1, 2022

So I have figured out a solution for me. Have continued issues with the TT and blown #84 fuse, I ended up adding a direct ground from the trailer to the truck. Frame to frame ground. That solved all my problems. So now ontop of the 7 pin connection I have another wire (which I use quick connects for), that is a dedicated ground from TT frame to the truck frame. No issues anymore.

Good luck everyone...

Colan · November 8, 2023

2020 Duramax 3500

Using a Curt adapter for LED lights on new 5th wheel, all but the left turn signal is working.

Trailer turn signal wiring checks out, connected to another power source, through the trailer seven pin cord everything works.

With the adapter and the right turn signal on, with a volt meter you can see voltage bounce between 12 and zero as expected.

Left turn signal on, nothing.

Here is where it gets really weird.

Plug the Curt adapter into the seven pin receptacle on the bumper. Plug the trailer 7 pin connector into the receptacle in the bed. Everything works as expected.