Highest ac/heat fan speed not working?

What is your question?

The 4th fan speed for the ac on my 2003 explorer sport trac is not working. I have replaced the blower motor resistor and the interior switch itself...along with the pigtail wiring with it and the 4th speed still doesnt work. 1-3 work perfectly fine, but now I'm lost as to what I should look at next?