Where is the coolant sensor that controls the dash gauge in 1987 Mazda B2000 truck?

The coolant temp sender that shows the gauge working temp is mounted below the upper radiator hose.It is mounted below close to the thermostat housing.It has a single wire terminal that slides on the connection.To replace is simple,drain coolant down enough so no fluid is in the upper hose,unless you plan a coolant flush(I recommend) unless your coolant is less than 3 yrs old.Now take terminal off,unscrew sender with a wrench.I suggest using some permatex high temp thread sealant(sold at auto zone,advance,napa) in a white tube.Place a small amount on the threads of the new sender and install snug,do not over tighten.Connect electrical plug,refill coolant system,and bleed air off,with truck at idle temp selector on heat,fan hi for 15-20 leave radiator cap off until coolant starts to bubble over then put radiator cap on.You might consider replacing your thermostat at this time as well and use a new gasket.If your hoses are over 4 years old replace those too being winter is coming,and are prone to failure on temp change hot,to cold either way.