I am trying to locate the Coolant Temp Sensor (ECU) 1989 G20 on 1990 Chevrolet G Series Van (G20)

Shop tells me the coolant temp sensor voltage =0, and the thermostat is stuck open. I believe the thermostat is located on the engine block @ radiator return, but cannot find the coolant temp sensor. Can someone describe where to find it?

Asked by for the 1990 Chevrolet G Series Van (G20)
its right next to the thermostat housing.