Recently, the heat/air fan on my sister's '99 Zetec ATX started only working on high, no matter where the fan speed knob was set. Instead of paying $75/hr for a mechanic to troubleshoot and fix this, I fired up CEG and found that it is a common problem. My local Ford dealer had two of these in stock, I believe the price was around $16. I noticed a lot of "where is the blower resistor" threads, so I thought some pictures could help.
It's located in the front passenger footwell. It's an awkward place to get to, let alone take a picture of, so I tried to take several. In this picture, the tan piece you see is the center console, and the part we're looking for is the white plastic part with the four-wire plug facing the firewall:
Mine was held in by a single torx-head screw, it wasn't too difficult to get out. If you don't have a torx bit handy, an appropriately sized flathead should work.
Here it is with the resistor pulled out:
Here's what a bad resistor looks like:
Somewhere along the line, Ford redesigned this part. Here's the old one compared to the new one, you can see that the plug is rotated 90 degrees, but it's not a problem:
Here's the new one installed:
Once you manage to cram yourself into the footwell somehow, replacing this part takes all of five minutes.