The 300ZX Shop Manual has one page visual for all the components, the sensor located on the drivers side just to the right side of the Distributor. Its screwed into the block near the top of the block and has two fine wires coming out of the sensor.
diagram of a nock sensor in a 300zx 1996
You are low on coolant or the low coolant sensor/wiring/connection is bad.
It is easy to find a repair CD for your zcar on the auction sites.
what sensor?
Check out 300zxclub.com
try ebay, search 1985 300zx for the Nissan Service Manual, I have the 1986 manual , it contains the wiring diagram
autozone
the little ye;llow sensor ontop of the metal coolant tube. theres 2 in the middle of your engine the top metal tube will have a little yellow senso that you screw out and just screw in the new one i believe the sensor is a 17mm wrench gl with ur z
http://www.300zx-twinturbo.com/cgi-bin/manual.cgi look through the service manual.
There is a large online manual at http://300zx-twinturbo.com/cgi-bin/manual.cgi Full of tech data I use as the "bible" for the 300zx. Hope that helps
When changing the thermostat on a Nissan 300zx first drain the coolant from the engine. Then find the lower coolant hose on the radiator. Trace the hose to the thermostat housing. Remove the housing to uncover the thermostat and replace the unit with a new thermostat.
The Nissan shop manual has a complete wiring diagram, they can be found on e-bay.