I also own a 2000 jeep grand cherokee and am about to replace my fan relay switch for the 3rd time...what i found out today is the contacts on the connector plug can burn off and they make a replacement connector for this... i'm guessing there is a cycle flaw of sorts from the computer to relay as my waterpump and thermostat and fan have all been replaced... this seems to be a real common problem...i'm going today to buy new connector and relay switch and see if it fixes it totally... will post how i make out.