Well, got a bit more time to work on the new system.. (should have been done by now...cripes!)Put the new ATX 400W power supply in place and plugged in all the matching plugs to MB (except the extra one for "Rambus"(?) boards)I still have two small diameter wires left to plug in. These are the size of fan wires and are color coded black and red just like most fan wires. They have a two post plug. All the fan power plugs on the ASUS mb have three wire plugs.Now, I'm thinking that they are for sensing either temps or fan speed (this mb connection IS two pin)in the PU but really have no idea, although it seems that if they are other than pos & neg power supply then they should be other color codesMfg website is being slow in an Email reply so thought I'd ask here also... Do all ATX power supplies have these two wires and if so, just what are they for. Best,

They're used for running the PSU fans :)

So just direct 12v supply when power is on then ? No MB "smart" control?Why don't they just run them from internal power supply juice I wonder...

They're the same wires as the fan on the heatsink, right? Or are they slightly bigger? some PSUs have another connector for P4 boards too.

http://www.formfactors.org/FFDetail.asp?FFID=1&CatID=2http://www.intel.com/design/motherbd/atx.htmNeither site talks about a two pin connector. However, after replacing a powersupply, I have two connectors unused on my system. One is the 12vdc power connector used on some MOBOs and the two pin connector. I believe the two pin connector is a fan speed monitoring connector that may be on some MOBOs. I won't willy-nilly connect this connector unless you are sure of its use.W. Sieffert

>Neither site talks about a two pin connector. However, after>replacing a powersupply, I have two connectors unused on my>system. One is the 12vdc power connector used on some MOBOs>and the two pin connector. I believe the two pin connector is>a fan speed monitoring connector that may be on some MOBOs. I>won't willy-nilly connect this connector unless you are sure>of its use.>>W. SieffertHmmmm, could still go either way :-( Are yours red & black code?Your power supply fan DOES come on without these connected right ?John,Mine ARE the small diameter size used on fan power apps. BTW

If they're the same size as the fan used on the heatsink, I can only assume they're for the PSU fans.. :)

>If they're the same size as the fan used on the heatsink, I>can only assume they're for the PSU fans.. :)Well... I guess I'll have to wait until after I power it up and see if the PSU fan runs without it or not.Better than adding 12v into the wires right from the start if they are not on a 12v area :-) "There's smoke hiding in them thar wires just waiting to get in your eyes" :-lol Thanks for all..

couldn't take a pic of them by any chance? :)

>>Neither site talks about a two pin connector. However,>after>>replacing a powersupply, I have two connectors unused on my>>system. One is the 12vdc power connector used on some MOBOs>>and the two pin connector. I believe the two pin connector>is>>a fan speed monitoring connector that may be on some MOBOs. >I>>won't willy-nilly connect this connector unless you are sure>>of its use.>>>>W. Sieffert>>>Hmmmm, could still go either way :-( Are yours red & black>code?>>Your power supply fan DOES come on without these connected>right ?>>>John,>Mine ARE the small diameter size used on fan power apps. BTWPlug-ins on the mobo that are RPM monitoring have to be three pin. Two for the power and the third is the monitor. Two pin plug-ins will run your fan but won't monitor in the BIOS. David

>couldn't take a pic of them by any chance? :)Sure I could if you think it's needed.. although you will only see one red and one black small diameter wires tied together and about 12" long, going to a small two prong female connector :-)Current update:Powered up new system without connecting these wires to anything...PSU fan runs just fine. BUT, still would like to know what these wires are for. Only one fan in the PSU BTW :-)Seem to be having some new problems getting things up and running now...Will post in a new subject so things don't get TOO muddy in this one :-)Best,

Plug-ins on the mobo that are RPM monitoring have to be three pin. Two for the power and the third is the monitor. Two pin plug-ins will run your fan but won't monitor in the BIOS. DavidNot quite. If the fan will be powered from the MB header, and has speed monitoring, it needs three wires (power, speed sensor, and ground). If the fan will be powered from the MB header, but does not provide RPM information, there will be two wires. Similarly, if the fan is providing RPM to the MB, but receiving it's power elsewhere (like a power supply fan, or a case fan connected to a 12v power supply cable), it will have only two wires. You can tell which situation you have by looking at whether the two wires are conntected to pins 1-2 or pins 1-3 on the plastic connector. There should be a diagram in your motherboard manual that shows this. Attached is the diagram from my Soyo manual.The last two power supplies I've installed have had two wires coming out, similar to yours. Since the wires go to pins 1 and 3 on the MB, I know they're for speed monitoring on the PS fan. A power wire is not needed since power comes from the PS itself. When plugged in, the PS fan RPM appears in Motherboard Monitor, or the Soyo hardware monitor.Edit: I just looked at the pdf version of your manual on the Asus site. It looks like you have a PS fan monitor connector near the "northwest" corner of the MB, which is a 3-wire connector like I described above. There is also a PS thermal sensor header near the southeast corner of the board, which is a 2-wire connector. If the wires coming out of the PS go to a 3-pin connector, with the center pin empty, then it's a fan RPM monitor. If they go to a 2-pin connector, it's a thermal monitor.

>Plug-ins on the mobo that are RPM monitoring have to be>three pin. Two for the power and the third is the monitor. Two>pin plug-ins will run your fan but won't monitor in the BIOS.>>>David>>Not quite. If the fan will be powered from the MB header, and>has speed monitoring, it needs three wires (power, speed>sensor, and ground). If the fan will be powered from the MB>header, but does not provide RPM information, there will be>two wires. Similarly, if the fan is providing RPM to the MB,>but receiving it's power elsewhere (like a power supply fan,>or a case fan connected to a 12v power supply cable), it will>have only two wires. You can tell which situation you have by>looking at whether the two wires are conntected to pins 1-2 or>pins 1-3 on the plastic connector. There should be a diagram>in your motherboard manual that shows this. Attached is the>diagram from my Soyo manual.>>The last two power supplies I've installed have had two wires>coming out, similar to yours. Since the wires go to pins 1>and 3 on the MB, I know they're for speed monitoring on the PS>fan. A power wire is not needed since power comes from the PS>itself. When plugged in, the PS fan RPM appears in>Motherboard Monitor, or the Soyo hardware monitor.Hi, I'm (Tom)the one with the original problem not David..Just wanted make that clear before David had to :-)One thing to take into consideration here... MY two wires are attached to a two wire plug.. side by side, so they could be plugged into a three wire mb connection either way :-) Also fully backwards if you like.. this is NEW 2003 ATX PS so should be up to date for connectors, so why the two pin ? I don't know..Anyway, as I've stated already I powered up the new system and the PS fan works with the two wires hanging loose so they are NOT power to the PS fan. NOW... if they ARE for fan rpms or temps ,I still need to figure out where/how to connect them.. I certainly COULD plug them into the empty mb connector for "PWR FAN" but would still need to know color code since they are only red & black. Black ground & red sensor pin ?Thanks for the reply,

Yes my PSU fans work, I think the two wire (black/red) connector is for fan speed monitoring, much like the CPU/CASE fan speed monitoring.W. Sieffert

>>The last two power supplies I've installed have had two wires>coming out, similar to yours. Since the wires go to pins 1>and 3 on the MB, I know they're for speed monitoring on the PS>fan. A power wire is not needed since power comes from the PS>itself. When plugged in, the PS fan RPM appears in>Motherboard Monitor, or the Soyo hardware monitor.Yeah,now that you mention it I think your right. I think the twisted- off color wires that are for the power supply RPM monitor did only have two wires but it was a three pin connector to the mobo--this is on an Antec power supply. I use Vantec 80mm case fans,those are two wire but their pinned 1,2.David