B Series Truck Coolant Temperature Sensor Location (1990)
Coolant Temperature Sensor/Switch (For Computer): Description and Operation
PTC Heater System
The Water Temperature Switch is an "ON/OFF" switch located in the bottom of the radiator. It is "ON" at temperatures below 15 - 19°C (59 - 66.2°F),
signalling the ECU to activate the carburetor PTC heater system.