The switch is located on the INSIDE of the C-channel frame rail, left side under the floorboard. To access it, the floor must be removed. It's not as bad as it looks. Remove the pedal (2 13mm nuts) then remove the floor. I have done it without removing the floor but it wasn't fun and wasn't pretty. If you wash that area out really well, sometimes it'll prolong the inevitable.
The grass clippings build up in that area and the moisture from the clippings gets into the switch and damages the contacts. That or occasionally the switch plunger won't extend because there is so much stuff built up behind it.
While you have the floor out, if yours has a flip-up access panel for access to the deck gearbox, look closely at the part that flips up. On the side closest to the front, right in the middle there's a piece of what looks almost like angle iron. If you look close, you may see where it rubs the deck gearbox a little when in the closed position. If it is rubbing, cut that portion out of the floor cover, just a notch is all it takes. I cut about 3-4" inches length and about 3/8" to 1/2" deep of it out so it won't rub. If you leave it, it's possible that under the right circumstances, it can knock the plug out of the deck gearbox and then you lose all the oil-which destroys the expensive gearbox. The newer ones already are notched from the factory.