To plug in, or not to plug in.

[Underhanded]

I am extremely unfamiliar with Intel motherboards. So when I built my first intel rig the other day (in my sig). I came across some strange things I hadn't encountered before. After full installation and days of troubleshooting, the system is still very unstable.. though it seems to have evened out the last few days.. I still have some questions about my motherboard.
The question I have is.. this motherboard has an ATX 12v connector on it, a 4 pin one that all ATX motherboards have pretty much. But IMMEDIATLY next to it, there is another 4 pin connector, covered by a small plastic cover, that is easily removed.
My question is, for normal ATX gaming rig operation, should both of these just be plugged in? Or should only the one be plugged in.
I checked the motherboard manual, and it said something like both for ECS, 1 for ATX, so I just left it (Since I'm also unfamiliar with ECS.. )
But seeing as how my system is fairly unstable... I'm starting to wonder if I should plug that sucker in... Thought I'd ask here first. Don't want to fry it or anything.
Here is a picture for reference.
Asus P5B mobo, plug in question circled in red

[jer888]

if the system works without it, then it proboly dosent need it and the instability can proboly be attributed to something else. what kind of instability symptoms are you having?

[Underhanded]

http://forum.pcmech.com/showthread.php?t=167422

[blue60007]

It's probably for an optional EPS 8pin power connector. The cap is probably there so you plug the right end in if you don't have a power supply with the EPS connector.

[Underhanded]

Ahh.. Righto.. My psu has an 8 pin.. that splits into 2 four pins.. but I think I've found the problem. Finally got it to crash again (playing WoW of all things)
Got it to bsod, found out it was my sound card drivers. Uninstalled them, haven't had any more problems (well.. no sound x.@)
Gonna tinker around with that problem today =P

[chuck4456]

That's a test socket. The manufacturer uses it when a board is returned to check supply voltage and contunuity.

[Underhanded]

Problem solved. The Soundmax drivers that I installed for the onboard sound are conflicting with something. Or are just downright broken. I uninstalled them, and installed an old soundcard I had lying around. No problems so far, everything is working as intended.
Going to just replace the onboard sound with a pci card. should have done that anyways..
Thanks for the help guys~ good to know what those pins are for =P