Hey and welcome to NICO Club!
I think your car is equiped with OBD-2 systems in addition to OBD-1. So, you should have a consult plug/port somewhere under the dash and you can use a code reader to get a code number. This will help you know which sensor is sending a 'bad' signal and confirm the direction you want to go with your diagnoses. On my car, which is a 1995 Nissan 240sx, the consult port is on the passenger side, near the transmission tunnel, just up under the lower dashboard lip.
The FSM can be downloaded from our website. See the "Service Manuals" link at the top of this web page. The EC chapter is all about engine sensors, the computer and related electronics. This often has the info for check engine lights. Some transmission issues will be in there and most others will be in the transmission chapter called AT. Aha!, Page 33 of AT will have inhibitor switch information. Here's a direct link:
http://www.nicoclub.com/service-manual? ... _Sentra/at
Finally, since you're on the internet, search for your "1995 nissan sentra neutral safety switch" go to shopping to see the price and mostly to see a picture of exactly what you're looking for. Next, go to your car and look at the transmission, near the pan and you should see the switch.
