89 4.0 electric fan ... switch or relay ???

My fan will only run when the AC is on, no matter how hot the coolant gets.

So the fan obviously works, and the gauge also works so I know the sending unit is good. As far as I can tell that leaves the wiring, or a fan switch if it has one ..........

Can anyone tell me where to start looking for a switch or relay on this ?

Man, I gotta find a set of factory manuals ........... :doh:


Thank You ! :cheers:

If your standing in front of your rig its to the right of the fan and below the wires to the fan.

there are two diffrent sending units.
The one for the fan is in the radiator...if you still have the closed system.
The one for the gauge is in the rear of the head.

It is common for there to be air under the temp sender in the head causing a higher temp reading on the gauge.

What Jess said. The one that controls the fan is in the radiator end cap on the driver side, about half way down. Big brass looking thing with a 2 wire harness coming out.

If you disconnect it and jump the pins together on the main harness side, the fan should come on (key on of course). If it does, you likely need a new sender.

Make sure you'r coolant is full too. Too low a coolant level can leave the sensor out of the hot coolant and it will never complete the circuit.