I have a 2000 Jeep Cherokee Larado 6 cylinder with 75000 miles and the cooling fan motor won't turn off. Can anyone tell me what the problem might be. Is there a heat sensor and relay involved and if so where are they located.

Yes there is a relay that might be causing your problem. Let it be known that Electric Fans can remain on after shutting off engine, this is to help cool down the engine (if it overheats), ussually it will remain on for a few minutes then shut off, if yours remains on longer then that then your relay might be bad. I am not exactly sure of the location of the relay but I do believe it is behind one of the headlight assembly.