Temperature Gauge not working! Please Help!!

Im not familiar with pre 99 stangs so I dunno if I can help much but I would start by checking the wiring that goes to the sensor,good connections,use a volt meter to check for power to the sensor.Did you drain the coolant when changing the sensor,if not and the gauge worked before I dunno why it would have and air pocket and if it did I would think that it would still be getting hot or at least thats the way it was on the alll the older Z28's and TA's I owned would do.
NM,taking out the sensor opens the system....duh,I wasnt thinking on that one.

Also the stock temp(all gauges) gauge really isnt good at all,its just a fancy idiot light,it reads if its cold,normal running temp, or really hot...not much in between,A cheap mechanical temp gauge would be more accurate than the stocker.

the 96 use 2 sensors, one that goes to the PCM (L) to turn the fan on, the other (R) to the gauge on the dash. which one did you swap out?