Sorry for the late reply. My bike is a 14' CB500F, but this part should be the same for the 300 F,R,X as well as the 500 F,R,X. I found a lot of posts, but ultimately just looked at the service diagram to figure out where it was and how to replace. It really is a simple install. Here is a quick write up:
1: Remove the left-side peg/plate cause that gives a little more clearance, and then remove the shift linkage (I used a crayon to mark the position so I could put it back on exact).
2: Right where the linkage attached, there is a round rubber boot, that is the Neutral safety switch. Pull the boot back and remove the nut that holds the wire on. Then remove the switch.
3: Then just reverse the steps to install.
Hardest part was getting the little wire/nut on the new one and getting the boot back on. Total time is like 10min.
I didn't have a pic, but marked up this one that "Nigel-on-Bass" posted here
The blue is the shift linkage you remove, and the red is the boot covering the Neutral safety switch.