I say probably yes to needing that connector, specially since it is a genuine Intel board. Most ATX PSU from 2000-2004 came with that AUX connector iirc (yes see 4 sitting in my stack with it).
They have a standard pinout for Intel based and carries 3.3v and 5v plus ground...

CC-Adam wrote on 2025-06-22, 19:13:

Found this board in a scrap bin so don't know if it works! I don't have a PSU with the auxiliary connector (see photo) it's like half an old AT PSU main connector. It doesn't POST, I get a green light near AGP socket and the fans spin up as soon as you apply power. There are no beeps and nothing appears on the screen. I'm wondering if that power connector is essential, manual doesn't seem to say much about it. I get 3 long beeps if I remove the RAM so it is showing some life. I've tried 2 different sets of RAM and two graphics cards. CPU is getting warm, it feels like it could work! 🤞 I'm hoping it's the connector, what do you all think?

Doubt it's the lack of the AUX (1 x 6) connector cable being present that's causing the POST failure...board should definitely complete a minimal boot setup without it. The following info from Intel explains further -

The 1x6 Auxiliary Power Connector is in place to provide support for AGP Pro 50 cards. Because AGP Pro 50 cards require more amperage than the ATX standard is designed to deliver, the Auxiliary Power Connector delivers an additional 12 amps to bring the total available to thirty. This cable, according to George Alfs (Intel Press Office), is not necessary if a board does not support the AGP Pro 50 standard.

Was also covered in this thread - PSU for Intel D850GB Pentium 4 Willamette.

What are the specs of your system - processor, memory, PSU?

I agree with PC Hoarder Patrol, I also don't think the no-POST issue is from not having a 6p AUX cable connected... but you can actually check if you have a multimeter. 😀

IIRC, those 6p AUX cables are comprised of 3 extra grounding wires, 2 extra 3.3V (orange) wires, and one extra 5V (red) wire. With that said, if you set your MM to continuity and you can see that the 3.3V lines on the 6p AUX connector have continuity to the 3.3V lines on the ATX connector, and same with the 5V line... then the 6p AUX connector on your board is really only extra redundancy to provide more current... probably for things like AGP Pro, as mentioned above... which is not present on your board. On the other hand, if they are not connected, then that would be an issue as probably the RAM or chipset regs may not be getting power.

So start with checking the line connections on that 6p AUX connector. If all is good there, then post the CPU sSpec #, RAM type, and PSU brand and model, as suggested above.
Also check your CFR2032 CMOS battery's voltage. Some OEM boards do not like to start properly when those are dead / exhausted. In the case of Dell mobos from the latter P4 era, the auto-start is normal when CMOS settings have been lost (due to bad or missing CMOS battery), but the boards usually POST fine.
While at it, also check all of the board jumpers and even remove and reinsert them a few times, just to make sure they make good contact. On that note, do the same with the RAM and CPU. Sometimes contact oxidation may form when the hardware has been sitting around in storage for very long.
I don't think the issue would be cap-related - the motherboard's CPU VRM appears to use UCC LXZ caps on the input and Sanyo OS-CONs on the output, so those should still be fine. The smaller caps around the RAM and chipset, especially those near hot(er) regulators may be at slightly more risk of being aged from heat... but I still find it unlikely. I've removed a bunch from similar scrap Dell motherboards, and I don't recall running into any that were failed. Maybe a few were just starting to get marginal, but that usually wouldn't be enough to cause issues.

Thank you so much for your help guys, it is now posting! 😁😁😁😁 There was indeed continuity from the aux to the main ATX connector proving it isn't required at least on this version of this board. I think the POST issue was bad RAM or dirty RAM slots as the last thing I changed was the RAM, although I'd already tried 4 different sticks, luckily I've squirrelled away quite a few RIMMS over the years, I didn't think I'd ever find a use for them though. I've even found a couple of 512MB sticks, they are different brands but the same speed, it POSTs with them in there so I'll memtest it soon to see if they behave together, although the mismatched brands will probably annoy me so I'll try and find a matching set of 4 but doubt they'll be 512's they seem to be quite rare.
I did also replace CMOS battery so could well have been this. After setting date and time I was greeted with a really cool Pentium 4 logo splash screen 😎

Thanks again to you all, most appreciated!

Thank you so much for your help guys, it is now posting! 😁😁😁😁 There was indeed continuity from the aux to the main ATX connector proving it isn't required at least on this version of this board. I think the POST issue was bad RAM or dirty RAM slots as the last thing I changed was the RAM, although I'd already tried 4 different sticks, luckily I've squirrelled away quite a few RIMMS over the years, I didn't think I'd ever find a use for them though. I've even found a couple of 512MB sticks, they are different brands but the same speed, it POSTs with them in there so I'll memtest it soon to see if they behave together, although the mismatched brands will probably annoy me so I'll try and find a matching set of 4 but doubt they'll be 512's they seem to be quite rare.
I did also replace CMOS battery so could well have been this. After setting date and time I was greeted with a really cool Pentium 4 logo splash screen 😎

Thanks again to you all, most appreciated!

Nice, good to hear the board is running again.
And yeah, that P4 BIOS splash screen is pretty cool indeed... though for my own personal system, I always disable the splash screens and let the board display all POST messages. IDK, I just like to see all of that when I boot up my PCs. I really dislike how modern PCs go straight to the Windows 10/11 loading screen with the spinning dots - booooorriiiing!

Thanks again! Yes I was well pleased to have this one working, it was rescued from the very bottom of a big scrap bin but it looked healthy and seemed to want to come back to life. Maybe being at the bottom helped it somehow. I always turn off the splash screen too although will be keeping this one for now. This board POST's incredibly quickly so you only see it for a second anyway.

I'm on a quest to find the quickest PC to boot Win 9x to a usable state from pressing the power button, which is currently a Tualatin P3 I I have running ME which takes about 16 seconds in total. This setup is a couple of seconds behind but better than most. Might start another thread about this I bet some other members here have some quick machines or tips for this.

Now I just need to find a sticker to match it for the front of the case, I've got one somewhere. The board seems to be rock solid stable, I've tried a few OS's all installed and running without a hitch, and several hours of memtest all perfect. I had a nice period correct ATX case ready for this if it worked, turns out it has a PSU inside with the AUX connector, doh! I had one after all just not in the massive box of PSU's I have, didn't think to check in there!!