I see it's been about two weeks since your last post. Can I assume you replaced the resistor and the fan worked properly for several days? If so you may well have an intermittent short in the harness.
I've posted a wiring diagram for a 96 in my Public Dropbox folder here
http://dl.dropbox.com/u/45028330/air-conditioning-manual-a-c-circuit-1-of-1.pdf
You can download the PDF file to your computer and open it in your PDF viewer. Most people are using Adobe Reader from
www.adobe.com .
As you'll see, starting at the top of the diagram, power comes from fuse 6, 50 Amp, in the Power Distribution Box. It then passes through the Blower Motor Relay contacts as the relay is energized when the ignition switch is in the Run position, putting power on the Pink wire with the White stripe to the blower motor. It then leaves the motor on the Brn/Org wire and goes to the normally closed contacts of the High Speed Blower Motor Relay. That relay won't be energized unless you select Hi on the fan speed selector switch on the dash.
The Org/Blk wire carries the power to the Blower Motor Resistor.
It's from this point on you may have a problem with a short or partial short that's putting too much load on the Blower Motor Resistor.
When you look at the Blower Motor Resistor in the wiring diagram you'll see two dark points/spots with a curved line between them. That's Ford's way of indicating a non-resetable circuit breaker in the resistor. If it trips you have to replace the resistor assembly.
I'd think your problem is in the wiring from the resistor to the fan speed selector switch, the fan speed selector switch itself, the wiring from the speed selector switch to the dash selector control that selects where the output air goes (the Heater-AC Control Assembly in the diagram).
Or your parts supplier is selling you less than good quality resitors?