Cutting fan yellow wire to disable fan speed control
 

Hi guys!
If I have a case fan with 3 wires to connect to the mainboard and the yellow wire is the one intended to controll the fan speed, will the fan always go 100% speed if I just cut the yellow wire and connect it's connector to mainboard? I don't want the fan to have speed less than its 100%.

The scientific approach would be to cut it and see what happens.

First what would be the reason for this? can't you just edit the fan settings in the BIOS to 100% full duty cycle?
The answer to your question is no... depends what the yellow wire is for.. if its merely to tell how fast the fan is spinning then no, because the yellow wire has no way of setting the resistance, it just tells the computer or circit connected to it how fast the fan is going, the motherboard or separate fan controller has a variable resistor that is connected in series to your red and black wires so you may attempt to control the fan, if this is directly connected to the motherboard and has no fan controller then in the BIOS under power management set the fans to 100% full duty cycle, this will tell the motherboard not to put any resistance to the fan making it run at full speed at all times.