The blower motor resistor on a TJ/Wrangler  is behind the glove box, on the passenger side.

MY DISCLAIMER: PLEASE BE VERY CAREFUL AS I DO NOT ACCEPT ANY RESPONSIBILITY FOR ANY INJURY YOU MAY CAUSE TO YOURSELF!!! BEFORE DOING ANY WORK ON YOUR JEEP, DISCONNECT THE NEGATIVE CONNECTION TO THE BATTERY AND WAIT 5 MINUTES. THIS TIME MUST LAPSE TO FULLY DE-ACTIVATE THE AIR BAG SYSTEM. YOU DO NOT WANT THE AIRBAG TO ACTIVATE PRE-MATURELY WHILE YOU ARE WORKING ON AN ELECTRICAL ISSUE. THIS IS STATED IN THE  JEEP MOPAR MANUAL - THEY MENTION WAITING TWO MINUTES - I WAITED 5 JUST TO BE SURE.

In the Jeep, on the control panel, there is the "fan knob" that you use to select one of four blower motor/fan settings when using the air conditioner or heater. The first three settings run thru the resistor. The fourth, the highest setting, does not run thru the resistor but connects "directly" to the battery; this is why the fan will always work on the fourth setting. The lower settings are controlled via the resistor and will not work if the resistor is shot. You can only assume that the blower motor resistor MAY be shot. Why MAY? Because there is a possibility that the reisistor is ok, but the respective fuse is blown. The fuse is also located directly behind the glove box, that when the glove box is removed, you cannot miss the small fuse box. Check the integrity of this fuse before you pursue replacing the blower motor resistor. On the glove box, on the right side, is a sticker indicating which fuse is for what function and you can find the blower motor fuse using that diagram. Pull the appropriate fuse out and make sure it has not blown. If it has blown replace it and see if the blower motor then works properly. If the blower motor does not work, then purchase the resistor, it costs approximately $20.

The wires that connect the "fan settings" control knob to the blower motor resistor are held by a wire harness. This wire harness attaches into the back of the blower motor resistor. (Once the glove box is removed, this can all be seen by looking into the void, to the lower right.) This wire harness must be removed from, and prior to removing, the blower motor resistor. For me, it was very difficult to remove the wire harness from the blower motor resistor as it was basically stuck in the resistor and there is not a lot of room to work with. BE SURE to un-lock the red wire harness lock located on the bottom side (it can only be seen if you view everything from the bottom up) before pulling out the wire harness from the blower motor resistor. Once the wire harness is out, you can then work on removing the blower motor resistor. There are two small screws/bolts that hold the blower motor resistor in place. Unscrew/unbolt the two screws/bolts, one on the top left and the second on the lower right. You can then pull the resistor out and insert the new one. Install everything by reading the above backwards.

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