i have a 99 jeep grand cherokee 4.7 v8. the electric fan work fine if you put 12v to it. I changed the relay under the right hand side headlight and check all the fuses. What else could it be?

 

It may not be getting a signal from the PCM. Check all your wiring for cracks, wear spots and corrosion. The PCM detects engine temp and sends a signal to the relay. Likely trouble spot in under the battery box.

 

Thanks will have a look

 

I checked out the wiring, would not wish that upon my worst enemy. I could not see any problems. I am now wondering if i should wire the fan to run when the engine is on full time? has any one done this? if so how did you go about it?