ok, I'm debating what the volages are supposed to be for a motherboard fan header. Usually there are 3 pins on a fan header. Since a power supply supplies 5v, 3.3v, and 12v, you would think that the fan header would output a combo of these voltages. I know that one pin will be the ground. The other 2 on older systems I think would be 5v and 12v. My main question is this. I know that the fan speed on many systems is voltage regulated by the motherboard. I saw a site that said the 12v rail can range from 1v to 12v. When the voltage dropped below 1v, the fan would turn off, when voltage rises above 10.5 volts, the fan would spin at full speed. I'm curious what the other pin should be...a constant 5v? Or does that voltage vary too? I cant find any more solid info on this. Any additonal info would be greatly appreciated. In my job, we check voltages of the fan header and I need to know what voltages constitute a good fan header and what voltages are considered bad. PLEASE POST THE CORRECT VOLTAGES OR RANGE OF VOLTAGES FOR MOTHERBOARD FAN HEADERS THAT VARY FAN SPEED BY GIVING DIFFERENT VOLTAGES.