I bought several of the first run of K-Line O72 switches, then bought some more from a forum member. The metal bar connects center rail to switch power; you would remove it if you want to run fixed voltage. The fixed voltage plug of some Lionel switches would push a contact out of the way, for this switch, you have to do it. So one connector is center rail, and the other "mechanism power". If in doubt and you have a VOM, remove the strip and ohm it out.
For the other three contacts, one is connected to outer rail, one is connected to the insulated section on the straight path, and the last on the insulated section of the curved path. Then wires of the insulated sections go into the mechanism for the non-derailing feature, and these two wires go out to the controller. So the controller is just like you rolling a truck over the non-derailing feature, connecting one or the other to outer rail (or 'ground' if you prefer).
The control mechanism and the K-Line switch controllers have diodes and LEDs so that the correct LED comes on, and still works when operated off of AC voltage. As I recall, that is why the controllers are handed. If you use something like an SC2, you don't have to worry about any of that stuff.
I have seen poor connections for each of the four posts (5 minus 1 to the mechanism) to their respective rails. If you flip it over and look, you will see brass strips embedded in the plastic, and then a small screw that is supposed to touch or pierce the rail. I have have to resort to soldering a jumper wire at times.
I have also seen poor connections between the center rails. I soldered a piece of 14 gauge wire between all three, and weave it among the ties.
I have found that I have to cover one of the moving rails with tape. The person I bought the switch from was more clever than I am, he used clear tape. Something happens with engines with wide center rollers, but I can't remember exactly what it was. I just remember seeing arc marks on the backs of outside engine wheels and finally figuring it out. This is O72, I don't know about O31.