Most likely the left 2 Pins. Run a Program that Displays the speed in real time like Norton Sysinfo and shorten it...you will see. If not shorten 1+3.

You might not need to go that far.
Some motherboards could also be adjusted via a keyboard shortcut commend, like CTRL + ALT + + or CTRL + ALT + -

For a switch, you just need any SPST switch - a rocker, a toggle, a latching pushbutton, whatever works best for where you intend to mount it. If you have a 3-terminal rocker, that's probably an SPDT switch, which will work fine (just ignore the third terminal).

Well, before I mess with any switches, I tried shorting pins 1 & 2, 2 & 3, and 1 &3, and running Maxspeed. CPU speed didn't change, kept displaying 23-24 (it's an AMD 386-SX25). It could be though that the turbo switch doesn't do anything for the clock speed but might disable cache instead. I guess I'll have to run a game or something and try it from there to see if the speed changes.

Not sure if the turbo can be switched via keyboard commands or not -- I originally assumed it could not because it has the header pins -- but that's another avenue I can try. It's quite the no-name board, can't find a manufacturer anywhere.

Often turbo/deturbo messes with wait states.