My 2024 GMC 3500HD just had the Module Replaced and Won't Detect Trailer, and No Running Lights

Updated 10/22/2025 | Published 04/12/2025

Products Featured in This Question

Pollak Metal 7-Pole, RV-Style Trailer Socket - Vehicle End

(111)

$14.77

Curt 7-Way to RV Socket LED Circuit Tester - Vehicle End

(190)

$20.10

Question:

GMC Hd3500 2024. I had problems with trailer lights. Took it to dealer they changed module along with other things. So now I hooked it to trailer and truck doesn’t recognize trailer and the running lights don’t work. All other lights do work.

asked by: Trent

Expert Reply:

Hello Trent,

Since your other lights are working on the trailer but your running lights are not, have you tried to turn your headlights on? I know in my 2024 Chevy Silverado I have to have the headlights on in order for the running lights on my Ranger boat trailer to turn on.

If your 2024 GMC HD3500 is powering the trailer lights but not recognizing that a trailer is connected, it usually comes down to how the truck detects the trailer. Instead of just sensing that something is plugged into the 7-way connector, the truck looks for a specific electrical load on the lighting circuits. If your trailer uses LED lights, which draw very little power the truck might not “see” the trailer even though the lights work fine. Another common culprit is a weak or corroded ground wire; the truck needs a solid ground connection to fully recognize the trailer. Since your trailer lights are working, it’s possible the module is sending power, but a poor ground or a missing load on one of the circuits (like the running lights) is preventing the system from fully detecting it. Also, if the Trailer Lamp Control Module was recently replaced by the dealer, it might not have been fully programmed or initialized yet. Testing with another trailer or a 7-way tester like # C73NR can help narrow things down quickly.

Let me know about the headlights and if you were able to test the 7 way and what you find out.

expert reply by: Kate F

Kate F.

10/22/2025

Hey Trent, what ended up happening after you tried turning on the headlights and testing the 7-way on your GMC HD3500? Did that help the truck recognize the trailer and get the running lights working again? Your update could make it easier for others troubleshooting similar light issues.