dougefish

Hey all. I have a 2015 3500HD with the trailer brake message. I am told by the dealer that there are two modules that look exactly alike, but only one is for the trailer brake controller. I found one of them, thinking it was the correct one, and replaced the module, but this did not fix the issue. This truck has a service body, and a second gas tank where the spare tire would typically go. Dealer states that the second module should be above the spare tire location where the additional fuel tank is now located. I looked above the tank as best I could, but could not locate the other module. Can anyone tell me where it could be located? The one I replaced was easy to find. It was on the front of the rear fuel tank, next to the fuel pump control module. As for module I'm looking for, can anyone give me some insight?