Blower motor in 1989 Mercury Sable Wagon

I've heard that, but the problem is reaching the motor itself. I believe its under the stereo in the middle of the dash board, but I cannot figure out how to remove the plastic shielding underneath to reach it. I have removed two screws from it but it will not budge.

I set my voltage tester to read 20VDC or less and checked across all three of the coils on the resistor itself, as well as all of the pin combinations for all 4 of the pins in the wiring plug that attaches to the resistor. I read somewhere that the resistor will have a constant 12V positive power feed to it when the key is turned on, and that it switches to a negative feed to activate the resistor and feed the necessary power to the motor for each speed setting. I wasn't able to detect any voltage across any of the pins. Am I putting my leads to the correct places or is there a certain way to test it that I am missing?