Those switches are quite good, and can come in a few different arrangements. The four pole variant means it has four channels - you'll probably only use one or two of them for the probe wires, but if you got creative one of the others could be used (e.g.) for switching some indicators to show which sensor is active.
The 'common' pin for each pole/channel is usually towards the centre of the switch base. Each common is teamed with three pins on the outer ring - the common makes with each of the three in turn as you rotate the switch (as do the other commons with their three at the same time). So your STC sensor terminal would be connected to a common, and your three sensors would be connected to the three outer pins associated with that common.
When you remove the panel-fixing nut, take care not to disturb the special washer thing below the star washer. IIRC it has a little inward-facing peg which limits the travel of the rotating switch to (in this case) three positions. It can be put back easily enough if it does come off, but its another thing to work out the correct position of.
There is a likelihood that your STC will throw a wobbly during the transition between sensors, as they are designed to notice sensor problems. I can't actually remember if the STCs self-reset once the sensor is reconnected; could be worth testing/verifying as it may be annoying to manually reset after switching sensor. EDIT: ignore that, I just tested mine and it did reset itself when the probe was reconnected. It also took a little while to notice when I disconnected the sensor, so its possible you could flick the switch without it realising
cheers
Kev
