I have a 2019 GMC Sierra SLE. and found the same issue with my Furrion 3 camera set. After some playing around I found that if I jumper the trailer 7 way connector Batt and tail/marker light pins the cameras will operate. but not plugged into truck. After research I found that their is not enough current (power) to power the cameras. I installed a relay where the trailer light is connected and use the 12v to power the tail/marker lights. The relay coil is energized by the truck tail lights so no damage will be done to the truck trailer control module. Problem solved.