I installed the Curt Spectrum 51170 with the wiring adapter in my '21 2500HD. It showed no calibration sequence LEDs (7 green flashes) and sent a constant 12v to the brake pins at the hitch outlet. Curt sent a replacement (very quick customer service response) and I replaced only the "brain", using the same adapter and knob from the first install. I still receive no calibration sequence signal, but the 12v feed to the brakes is gone. So, I'm making some progress. I have reached out to Curt once again, but, just wondering if anyone has had similar issues. Thanks.