The P8 and P9 power supply cables may not even go to anything.
The power supply cables coming out of the Power Supply, can be labeled, however that particular pre-built computer manufacturer, deems.
General labeling for the power supply cables is;
1) P1 - The 20-pin ATX main power cable, or 24-pin ATX main power cable.
2) P2 and P4 - The 4-pin ATX +12 Volt power cable
3) P3, P5, P6, P7, P8, and P9, can be used for a standard 4-pin Peripheral power cable, ('Molex'), or a small 4-pin Peripheral power cable, (Floppy Drives/Card Reader), or a SATA power cable.
Here, let me show you a basic example, looking at Power Supply cable connector markings, for the Dell Optiplex 745 Desktop PC,http://support.dell.com/support/edocs/systems/op745/en/UG_en/mt_pwrsp.htm#wp1109155
Scroll down look under the subheading - DC Power Connectors
This link shows you the various power cables, and their respective connectors,http://www.playtool.com/pages/psuconnectors/connectors.html
If the problem is a Tyan Trinity 400 S1854 motherboard, let's look at the power cables you need to connect;http://tyan.com/archive/products/html/trinity400.html
To the right of the blue bold - Trinity 400 (S1854) - heading, click on the Manuals icon.
Scroll down to the chart that has - Socket 370 (Intel Celeron / Pentium III ), at the top. In the list click on the blue -
[ Shows as Trinity 400 (Addendum)
You have the option to click on Trinity 400, or Addendum.
Do not click on Addendum at this time ]
This is a PDF file. The computer you are using now has Adobe Reader on it, which uses PDF files.
After you click on the file name (Trinity 400) it may take up to 30 seconds, before the first page comes up.
Using a medium speed DSL connection, it took 12 seconds just now.
(Wanted you to know, because you will be staring at a blank white page, until the first page comes up. Didn't want you to think the link doesn't work. The file is downloading in the background. The first page is the LAST to come up )
When you are staring at the cover sheet -
Tyan S1854 / Trinity 400 / Motherboard User's Manual / Revision 2.02 -
,bring your mouse cursor to the bottom/middle. The ghosted out navigation guide will now appear.
Go to the far right, and left-click on the Adobe PDF icon.
When you hover your mouse cursor over it -
Show Adobe Reader toolbar - comes up.
Easier to navigate around.
At the top, (Header), is the PDF file page number box. It is to the right of the Down Arrow.
To the right of it, is the Zoom In icon ( + ), and the Zoom Out icon.
( - )
Clicking on Zoom In increases the view size.
Clicking on Zoom Out decreases the view size.
Go to Page 13.
Bring the view size so you are looking at the entire motherboard illustration.
(For me it is 75 percent. I'm using a 26 inch RCA EN-V HDTV, as my main monitor)
You can use the Down Arrow to go page by page; Or,
1) Left-click once in the PDF file page number box.
Contents in the page number box will be highlighted in blue.
2) Type the page number (In this case -> 13)
3) Press the Enter key.
Page 13 is an illustration, Page 14 is a photo; Top View.
A) ATX main power cable.
It is a 20-pin ATX main power cable,http://www.playtool.com/pages/psuconnectors/connectors.html#atxmain20
Looking at the illustration it is shown at the far upper right.
ATX power connector.
It is in-between ram memory Slot 3 (DIMM 3), and the Floppy Drive cable's connector.
That is the only power cable that connects to the motherboard.
B) Your IDE (PATA) harddrive, will use a standard 4-pin Peripheral power cable,http://www.playtool.com/pages/psuconnectors/connectors.html#peripheral
DOES NOT MATTER what P number is on it, as long as it is a standard 4-pin Peripheral power cable, you're fine.
In fact you may have some of these power cables left over. Roll them up out of the way, and tie them with a plastic zip strip.. The inside of your computer needs all the air flow it can get.
(Bread tie = NO. It has a metal wire inside. Do not recommend)
C) Your optical drive/s, (CD/DVD drive/s), are probably IDE (PATA) also.
Each one needs a standard 4-pin Peripheral power cable.
Again, DOES NOT MATTER what the P number is.
You may have a computer case fan, (Or more than one), that has an adapter cable, allowing it to use a standard 4-pin Peripheral power cable, OR a small 4-pin Peripheral power cable, for power.
(In the Playtool link, the Peripheral power cable example, is a standard 4-pin Peripheral power cable.
The Floppy Drive cable example is a small 4-pin Peripheral power cable.
They are BOTH Peripheral power cables.
The Small, and Standard, are designations that allow you to immediately know what you are looking at.
Newer computers do not use a Floppy Drive. This power cable is usually used for a Card Reader. Hence the need to have a more standard designation, for these two types of power cables.
The Peripheral power cable has been mislabeled as a Molex power cable.
Molex was the first maker of this type of power cable CONNECTOR. The name stuck. Kind of like calling an adustable open-end wrench, a Crescent wrench )
Those small 4-pin Peripheral power cables, can be used for a myriad of devices. (Floppy Drive/s, Card Reader, power to a case fan, etc)
Again, as long as you find a device, that needs it, it does NOT matter what P number is on that power cable's connector.
A computer case fan is supposed to attach to FAN1.
The Brown three pin connector at the end of ram memory Slot 1.
(DIMM1) Power for the fan.
Same thing for the Brown three pin FAN4 connector on the motherboard, above the AGP expansion slot to the left, and to the right of the Game Port. (Joystick)
Same thing for the Brown three pin FAN3 connector, above the CMOS battery, and to the left of the VIA VT82C596B - Southbridge chip.
Same thing for the Brown three pin connector FAN2.
It isn't shown on the illustration, but is in the photo.
It is to the right of the Brown three pin FAN4 connector.
If all of your devices has a power cable, then P8 and P9 may not be used. Just extras in case you find devices that need them.
For additional questions please post in a Comment.
[Main thing is to have the jumpers on the motherboard, set to the correct setting.
Also, at the last make sure your ram memory module/s ('Stick'), are plugged in tightly. You can accidentally bump them loose, when plugging power cables in ]