No luck for me with Noctua fan unfortunately. But I suspect some defect with the WiiU itself. All fans always run at full blast for me. Tried Noctua, and Aliexpress replacement part which looks like original also same color wires.

No that doesn't seem right. If someone knows the pinout with some certainty, please do tell.

Is it red = +5V, black = GND, grey = ¿PWM? - can't find original fan to buy [don't want to order from overseas] so trying to go with a 40mm 5V replacement, reusing the original connector.