Grounding the Sensor
Most temperature sensors require a signal wire and a ground. Some sensors provide their own ground, in which case there will be two (or more) wires running to the sensor.
However, the vast majority of temperature sensors expect to get their ground via the body of the sensor itself. (If you are not sure what type of sensor you have, consult your sensor
documentation or factory service manual.) Most sensors of this type are screwed into the intake manifold, water pump or engine block, all of which are grounded.
However, when you install a sensor in the radiator hose, it is isolated from the engine ground by the rubber radiator hose. In order for the sensor to function, you will need to provide it with a ground.
Crimp a round headed crimp connector to the end of a wire (18-22 AWG size would be fine) Run the 18-22 gauge wire from this terminal to a convenient spot on the engine or body which is grounded.
(You will need a crimping tool to connect the wire to the terminal.)