# Convert 3 wire to 4 wire question (CPU fan)



## DannyB81

I am trying to replace a 4 wire fan on an emachines and I have a 3 wire fan from a dell, but my question is can I solder a 4th wire to my 3 wire fan and just change the connector? There is a spot labeled "sc" (speed control?) that is waiting for a wire but is it functional? Thanks


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## DannyB81

http://i40.tinypic.com/rbw84k.jpg maybe this will help someone understand what im talking about


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## Rich-M

Most likely no need to do anything as the 3 wire will run fine on the 4 wire connection.


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## GZ

The fourth wire is for pulse-width modulation, which is a special way to control fan speed. A three pin fan will connect directly to the four pin header and operate normally. The three wires are the power, ground and signal (fan speed) wires. The fourth pin on the header is for PWM and will remain bare. If you attempt to modify the harness in any way and connect the wrong lead to the motherboard you can damage both the mobo and fan. Just plug it in the way it is.


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