Neutral safety switch location

On the drivers side of the trans-axle, right where the shift cable attaches.
Normally they will start to get flakey, you have to jiggle the shifter while in park, or shift it in/out a couple times. Suddenly the car will not start, but if you shift the lever to half way between drive or reverse and neutral it starts.
Or the backup lights do not come on unless you move the lever a bit.
It should look similar to the picture.

Your car actually has a second switch to tell the computer you are in park as well. That one is under the console attached to the shifter. It is the one that lets you turn the key all the way to the lock position. If it fails you will not be able to turn the key all the way back to get it out of the ignition switch.