There are at least (2) - one on the driver's side head, and one on the intake manifold, there may be another, they feed the gauge, the ecm, and the radiator fan controls.
On intake manifold.
There's a coolant temperature sensor located on the lower part of the water pump on the drivers side.
The coolant fan switch is located close to the thermostat.
The 1988 Honda Accord coolant temperature sensor can be found on the front of the engine. The coolant temperature sensor will be a few inches above the thermostat housing.
The 1988 Dodge Dynasty coolant fan sensor is located a few inches above the thermostat housing. The thermostat housing can be found on the front of the engine.
passenger side of motor under exhaust manifold
Behind the timing belt cover.
located on radiator shroud on drivers side and possibly drivers side on fenderwell
A CORVETTE 1988 goes up to about 180
located on the passenger side of the radiator. Single wire (spade connector), I believe it is green in color.
There is not a separate cooling fan sensor, it controlled by the ECM which get it's reading from the ECT (engine coolant temp sensor)
It's right on top of the engine, next to the thermostat housing. Just disconnect the wire, turn out the sensor and replace it with a new one. If you need to add coolant, add the coolant after you change the sensor. Also, you should be ready with the new sensor as soon as you take the old one out, coolant will most certainly start to flow from the opening.