Hello... You need to determine what wires do what before just plugging in the connector. A four wire fan has...
12Vdc-Common-TACH-PWM
You can see/count the wires comming directly out of the FAN... I suspect it is really just a 3-wire fan... but you need to make sure. Your MB manual/PDF will have a wire diagram for your MB fan connectors.
A Wiki search for Computer fans stated this,
"Dell proprietary This connector is an expansion of a simple 3-pin female IC connector by adding two tabs to the middle of the connector on one side and a lock-tab on the other side. The size and spacing of the pin sockets is identical to a standard 3-pin female IC connector and 3-pin Molex connector. Some models have the wiring of the white wire (speed...