My 1999 jeep grand Cherokee is overheating. The electric fan won't turn on

Ok, now fix it.

I've been told there is a relay underneath the passenger's headlight support that controls the fan. On some models, they moved it or changed the circuitry.

Disconnect the power lead to auxillery fan, jumper wires to the batt. If the fan runs swap the relay under headlight as mentioned.

Replace relay first, if that doesnt work, replace fan as well. Make sure you buy replacement components with a lifetime warranty. By doing this, Ill never have to buy another relay or fan.

Jumping the fan is not a totally accurate assessment of the condition of the fan. If the relay is blown, and blown due to a high amperage draw from the fan, it will continue to blow relays. The fan should be checked for this high amperage draw. In Chryslers, infinite wisdom, they did not provide enough protection for this this relay circuit so, the relay takes the shot every time. This problem could also be the temp sensor. I have provided a link to a great article on how to diagnose these electric fan issues in these Jeeps. You also failed to provide the engine size as there are two different engines with two different cooling fan configurations. Here is the link, hope it helps:

http://troubleshootmyvehicle.com/jee...he-pwm-relay-4