Exactly... the switch is mounted on the pedal support, and by loosening the nut, you can slide it forwards and backwards, until the plunger is depressed when the pedal is relaxed, then tighten the nut. It works just like the plunger switch in the door. Door closed - plunger is depressed... door open - plunger extends completing the circuit and light comes on.
With this type of plunger switch, it wouldn't matter - it doesn't require positive and negative polarity. It simply makes contact internally to complete the circuit.
Where did you get this replacement switch? I'll try to post a picture of an original one tomorrow so you can compare them.