So I got the custom assembly together. 2024 2500 HD, used the #85573256 camera, genuine GM. Cable from Segemart. Camera works when plugged into the interior camera port but nothing in the exterior port. Tried a bunch of internet fixes and nothing worked. I finally brought the truck in to the Chevy dealer. They had the same issue and couldn't get it to work. They got a hold of one of the factory assemblies and it worked as soon as it was plugged in. Service advisor said they will eat the diagnosis time since GM won't reimburse for testing non GM part. Hoping this wasn't a waste of time and money but not looking good. Answers anyone?