OEM JZA80 Supra / JZZ30 Soarer / JZX100 Chaser Lower Radiator Temp Switch Sensor.
This sensor is screwed into the bottom passenger side of the radiator on turbo model cars and from memory (don't quote me on exact temp) at 90 degrees it sends a ground signal for the accessory fans circuit to come on and assist the clutch fan with cooling the car.
Note: This product comes in genuine OEM Toyota Packaging and was taken out for the photo.