My 1999 F150 193000 miles, is in great shape and runs great. The Blower motor control switch has four positions. The fan speed only increases in the last two positions. What can I do? Change the switch, Is there a relay?

 

Hi and Welcome to FTE!
...Thread Moved to the 1997 - 2003 F150 forum..

 

It well could be the switch,but my first thought(old school auto electrical) is there may be a "Ballast resistor" that controls the actual motor speed. These "resistor blocks" we placed in the air ducting system for cooling purposes.The resistors Im speaking of are actually just coils of wire in varying lengths.
The switch position routed B+ voltage to specific "taps" on this block that created resistance in the circuit,controlling how much voltage was eventually applied to the blower motor.
With ALL that being said,Im not sure if this applies in this case,but its worth a shot.

 

The blower motor resistor is located under the dash on the passenger side. Get down on the floor and look up. There is a four wire connector to unplug from it, then two screws to remove to get it out. Good luck!