Unknown 4pin connector

[petr.siska]

Hello, I purchased Cooler Master fan A12025-12CB-3DN-F1. It has regular 3pin connector but also some 4pin square connector (2 pins + 2 holes). Can anybody explain it's purpose for me? Thank you in advance. https://ibb.co/gohyAd

 

[Aeacus]

What you have is a Cooler Master Cosmos SE stock front fan and the 2nd wire is for LED control. Since when that fan is in the Cosmos SE case, case itself has a switch to turn on/off the LEDs of the front fans.
case specs: http://www.coolermaster.com/case/full-tower-cosmos-series/cosmos-se/

Cooler Master's Cosmos SE sports an easily removable dust filter in the front. Behind it, two 12 cm fans (Cooler Master A12025-12CB-3DN-F1) pull air into the enclosure. The fans feature blue LEDs you can turn on or keep off.

source: https://www.tomshardware.co.uk/cooler-master-cosmos-se-review,review-32886-3.html

 

[petr.siska]

What you have is a Cooler Master Cosmos SE stock front fan and the 2nd wire is for LED control. Since when that fan is in the Cosmos SE case, case itself has a switch to turn on/off the LEDs of the front fans.
case specs: http://www.coolermaster.com/case/full-tower-cosmos-series/cosmos-se/

Cooler Master's Cosmos SE sports an easily removable dust filter in the front. Behind it, two 12 cm fans (Cooler Master A12025-12CB-3DN-F1) pull air into the enclosure. The fans feature blue LEDs you can turn on or keep off.

source: https://www.tomshardware.co.uk/cooler-master-cosmos-se-review,review-32886-3.html

Thank you. After I connected these two pins with a jumper, LEDs turned on.