1989 Toyota Tercel Temperature gauge reading is increasing

I noticed today that the temperature gauge was reading higher than usual. Around the 10 o'clock level rather than around 8 o'clock, where the needle usually resides. When I had this problem before, about 8 years ago, the fan had malfunctioned. I did not hear the fan running today. I want to address this before it overheats and, looking in the manual, it gives some tests for the fan. One involves the temperature sensor switch. Does anyone have any ideas on how to locate the temperature sensor switch? Also, any other thoughts on diagnosing/fixing the problem?

Thanks!