So does this mean it doesn't throw the trailer warning now? Both versions, brake light and reverse light?
Well the C1 shouldn't throw a message about a brake light being connected. There is a resistor on the C1 that has to be CUT for it to work right (the resistor is required for other trucks).
The C1R on the 2015-2020 requires the new harness, which pulls the brake circuit from the tail light harness (which is how Putco does it actually on their tailgate bars).
The new harness is being announced today actually by Diode Dynamics but we were given a heads up about the new harness now to give our customers the chance to get their orders in with us.