The klipper harness is assembled with the intent of using the small triangles on the harness to locate the pins.
A rpi diagram courtesy of raspberrypi.org shows the pin numbers here
The harness comes with a diagram and shows the pin numbers. The main harness, the connector on the right in the below image, has the pin marked with a triangle go to pin number 2.
The harness connector on the left is for the accelerometer, and is not needed for the main install.
Connect the Panel Due harness in the manner that is described in the video below. Be careful of the orientation of the Panel Due plug you remove, and connect the power wires as described.
One of my Patreons is working on a presentation documenting the install, so I will add it when it is ready.