You can use that big switch to turn on an ATX system. Just flip it right back after your system starts.

Thanks. The problem is the switch connects directly to the PSU by a 4 core cable. There are 4 pins on the switch. These old machines didnt have power pins on the motherboard, So the switch at the front just turns the PSU on and off. I may not be explaining this very well. I'm still trying to figure it out.

But you're going to use an ATX power supply right? 😀

Connect two pins from that switch to the power-on header on a modern mainboard. Sometimes there is a schematic of the switch on the PSU. Or trial and error.

PD2JK wrote on 2024-02-17, 16:02:

But you're going to use an ATX power supply right? 😀

Connect two pins from that switch to the power-on header on a modern mainboard.

Okay I see what your saying. I'm not sure how I would connect such big wires to such small pins?

How are your soldering skills?
Do you have spare parts from old cases you could use? (hint)

PD2JK wrote on 2024-02-17, 16:16:

How are your soldering skills?
Do you have spare parts from old cases you could use? (hint)

Non existent.
And perhaps. I'm just thinking how small those power-on header pins are.
Thanks for your thoughts, at least I can see how its possible now.

There are momentary rocker switches - if it is important enough to you, you could probably find one that will fit the physical dimensions of the case. It would be the most elegant solution. I have an AT motherboard with an ATX power supply in an AT case and I took the easy way and used the reset switch.

https://www.google.com/search?q=momentary+roc … nt=gws-wiz-serp

Repo Man11 wrote on 2024-02-17, 17:14:

There are momentary rocker switches - if it is important enough to you, you could probably find one that will fit the physical dimensions of the case. It would be the most elegant solution. I have an AT motherboard with an ATX power supply in an AT case and I took the easy way and used the reset switch.

https://www.google.com/search?q=momentary+roc … nt=gws-wiz-serp

Thanks for the suggestions. If I can't figure out how to do it, I will use the reset switch option. I did find this which is interesting. Not useful in my case, but maybe for someone who wants to use an ATX PSU with an AT motherboard.
https://www.amazon.com/dp/B075ZPWJBX