Originally Posted by Al Mac
Any body have any other ideas. I have a 2004 FX4, and the blower works on 1, 2, and 3. It works on 4 but runs the same speed as 3, so basically I have 1, 2, and 3, and 3 again. I changed the resistor (ford part) today, but it did not fix the problem.
Your Blower Motor Switch bypasses the Blower Motor Resistor when turned on High.
You can check the resistance on the Blower Motor Switch(dash), or do it the easy way, Take it out, go to Advance or another parts store that allows returns, and put in the new one, if it works you are good to go, if it doesn't fix the problem, return it, you are just out your time.
Then I would Check the wiring from every connection from the Dash Blower Motor Switch down to the Blower Motor itself for corrosion/melting. Cleaning them with a can of electrical cleaner along your inspection.