Can Noctua fans be used with only + and GND connected?

All Noctua fans can also be used when only + and GND are connected. The fan will then run at full speed. 
Please note that modifications to our fans such as cutting the cables of a fan can void the fan’s warranty. This also includes out-of-specification use, such as reverse voltage. Further information on this is available in our warranty terms and conditions.

What pin-configuration do Noctua products use? 

All Noctua 24V, 12V and 5V fans, fan controllers, cables and other accessories such as Low-Noise Adaptors use the same standard pin-assignment that has been specified by Intel and AMD.

Pin configuration of Noctua 12V fans: 

Pin configuration of Noctua 24V fans: 

Pin configuration of Noctua chromax fans: 

Pin configuration of Noctua 5V fans: 

If you are looking for information regarding the implementation of PWM (Pulse Width Modulation) speed control in Noctua 4-pin PWM fans, please see our PWM specification white paper