Engine temp gauge not reading?

[SwiftThunder]

I recently put a better running 2.3l engine in my ranger and now my temp gauge for my coolent isn't quite right it stays above the bottom line when the engine is on but when off it shows dead so i know it is partially working. Which coolent sensor sends the info to the gauge the temp switch or the temp sensor and which one is on the heater core hose and what is the one in the side of the block, I really just need some assistance in this. Which is which??

[DonSor]

Your coolant tempt. sensor should be located in the vicinity of your thermostat (upper front of the engine). Once you locate it, disconnect the wire from the sensor. Turn your ignition key on without starting. You should have power in the wire. At this point your gauge should read max. Then short the wires to ground and again turn your ignition on. It should go minimum. If it does both, your gauge is OK but your sensor is bad. You may also remove the sensor and test it by reading resistance while immersed in hot water.

[SwiftThunder]

So the thermostat gauge is one wire?

[DonSor]

That's correct. One wire.