1991 Mercury Grand Marquis with a/c, 68K, mint condition.

I have a problem with the blower speed settings on my Mercury. LO (1), (2), and HI (4) work fine. Setting (3) is no different from (2), the fan stays at the same speed. I took the switch apart and everything looks fine there. I have a feeling that the blower motor resistor is the culprit. Where is it located on the car, and how would I recognize it?

 

You right about the resistor. It's in the evaporator box between the blower motor and the evaporator. I think on the Grand Marquis it's under the hood. It's usually made out of a fibre with a plug going into it with 5 or 6 wires in it. It's held in with 2 screws. When you pull it out it will have a series of different size coils on the other side.