To connect the power button and LED to the powerboard you will want to use the original power button cables and add Female GPIO to the ends of them. The yellow cable isn’t needed at the moment because the orange cable is used for both LED and reset switch. I chose to use it for the LED.
I soldered the GPIO cable ends to the original NES cables and then taped up the connection with insulation tape (you can also use heat shrink) as picture.
After you have done this, simply connect the cables to the power board. As pictured below.
Now the power button and LED should work when you turn the console on using the NES power button.
You will also need to connect two cables from the powerboard to the raspberry pi so the powerboard knows if the pi is off or on to control the power light. To do this you need to have 2 GPIO cables coming from the powerboard to the raspberry pi. I had to soldered the ends of the GPIO cables to GPIO pins 24 and 26 on the underside of the raspberry pi board due to the GPIO controller adapter being in the way. The adapter doesn’t use these 2 GPIO pins.
The full layout of all the cables from the powerboats.