what fan should you use for system fan monitor?

[sweeper2]

this may sound stupid, but i would like to know, what fan can i hook up for my system fan? Only have 2 hook ups on the mother board, 1 is cpu which is hooked up and the other is the system fan. Right now i have the PS hooked into it. I am running a rear case fan, that does not have a (yellow) sensor wire, a PCI rear fan that does not have a (yellow) sensor wire and a side case fan blowing on the PCI,AGP cards which does have the extra yellow wire. So its either the side fan or the PS fan...does it even matter? and what detects the actual temp of the system?

[Starfury_2260]

the motherboard should have temp sensors. what motherboard do you have.

[sweeper2]

Originally posted by Starfury_2260
the motherboard should have temp sensors. what motherboard do you have.

i use a k7n2 MSI delta L nforce 2 400 edition
think by looking at it, it only has 2 sensor hook ups, one for cpu and the other for system fan. Just trying to figure out what they mean by "system" fan. Is it the back case fan, the side case fan or the power supply fan?