Warning: Do this at your own risk. I will not be responsible for any issues. Make sure nothing is connected to electricity when doing this.(i,e. make sure everything is completely unconnected). If you do not, you will get electrocuted and die, so use common sense and be careful so you do not kill your working power supply and computer either. If you feel uncomfortable doing this, then get a professional to help you. Preferably you should not be color blind. You must know how to solder. Take your time making this cable.
To me the cable was not that hard to make but it did take a while. I also had to make sure of the safety precautions so no one or nothing was hurt and that I was accurate in connecting the wires..
Step 1: Whats Needed.
1 - AT Computer and monitor
1 - ATX to ATX cable Extension (Available a better computer stores)
1 - set AT wires (p8/p9) set from a dead AT power supply.
1 - Toggle On/Off switch (not a momentary switch).
Wiring diagrams for your ATX and AT power supplies. Yours may vary, so be careful. You may have to set up your own wiring conversion diagram. Mine is ONLY for the power supplies I used.
Step 2: What to Do.
2. Start striping ends and then start soldering wires per the diagram from the AT connectors to the female ATX connector and usually, but not always you will be soldering like colors together, (At least one set of the wires will not be the same color.) Follow the diagrams for your power supply.
3. At this point eight of the wires will be or should be un-connected. Now solder the switch to the power on and an extra black ground wire per the diagram.
4 Use electrical tape to cover any bare or exposed wires/ends or bare points on the switch.
5. Recheck wiring and of all is ok then use the electrical tape to bind everything up. (otherwise fix any problems so you do not fry your AT computer or ATX power supply.
Step 3: Use It.
I am actually building a robot and I needed this cable for that to connect to a DC -DC ATX PS. The robot is priority one right now for us.