you solder the 4 wires on the backside of the razor x pcb and they will then be soldered to the psp.
to assemble the nub you simply completly dismantle a psp nub and then take the spring, the part that connects to the nub cover and the top half of nub(part you pull apart). you then assemble just those three parts like you would as normal and put on your razor x pcb. move it around to make it sit in place and the razor x board should be flat against the plastic. then using heat melt mushroom down the 4 legs to the pcb and that holds it together