The engine died in my Cherokee. I love that car so I bought an engine from Craigslist, and had it installed. The installed engine has a sensor in the back of the head, drivers side. The engine that came out didnt have that sensor. The only other weird thing was the ignition coil; I had to swap the two, because they were different.
Now my fan doesnt work. The guy that swapped the engines said the sensor makes the fan work; because my wiring harness doesnt have a hookup, it doesnt know when to turn on. The Jeep mechanic said the sensor is only for the gauge, and the sensor on the thermostat housing makes the fan work. I think he's wriong cause my gauge works fine.
How do make that fan work?
Thanks all!
C

The one at the back of the head is fo rthe temp gauge on earlier models. Leave it there to plug the hole.

IIRC, the sensor in the thermostat housing has 2 pins, one for the gauge and one for the fan.