Fan speed switch probably not bad since it is sending 12V to motor. Resistance coils mounted up on outside firewall, dash air induction box, curb side, replacement was my problem solver last week for my 03 Windsor. Four wires plug into the top of the resistor . Unit held with 2 Phillips screws. My resistors were mounted inside a perforated metal cage to keep debris off coil. Resitor cluster is Ford, 4C2Z-19A706-BA. Bought Auto Zone RUC1006 did not fit cage and I had only 2 of 3 speeds. Googled and ordered Karpal 1KPFD 0107001. It fits cage and gives me 3 speeds along with the high speed.
My headlight switch dimmer not good. Rotated know multiple times to polish the resistance coils. All good now.