Instructions for what, to turn it on? Or for what wires provide certain voltages?
For pinouts, just google 'AT power supply pinout', and you'll get a lot of results,
here's one that looks good.
I'm pretty sure every AT PSU I've owned had its' own power switch, whereas ATX PSU's require you to jump 2 wires if you're not connecting them to the motherboard. What brand PSU is it?