A：The additional 4 pin connector is a sense relay, its main function is to help keep +3.3V, +5V, and +12V’s voltage regulation within ±3%. If you do not use it, the power supply can still functional normally, but with slight increase in voltage regulation range (but well within Intel’s ATX spec. of ±5%). You should connect this 4pin connector to the socket located above the 24 pin receptacle (pic 2). Pic 3 shows how the cables look when properly connected.