1989 Ford F-150 temp. Sending unit.

Hello and thanks for the donation!

Your vehicle's coolant temperature sending unit is located on the left front side of the lower intake manifold (for 5.0L & 5.8L engines) OR on the left front corner of the intake manifold (for 7.5L & Diesel engines).

Test the coolant temperature sensor, and inspect wiring

The reference wire that carries the 5 volt signal to the sensor will only read 5 volts if the sensor is disconnected. Any time the sensor is connected properly and the sensor ground is good, the 5 volt reference drops immediately. Usually, the voltage will be anywhere between 4 volts (very cold) to around .5 volt when the engine is fully warmed up. Room temperature will usually produce 2 to 3 volts (approximately 1/2 of the reference voltage). When the CTS circuit is open a scanner will read the coldest temperature that the computer can register in its program