Shut off the power to the HVAC unit at the main power panel. Check the manufacturer's wiring manual to verify blower motor wiring configuration and what size control switch should be used with it. Locate the black and white wires that will supply power to the motor.
Connect the white wire to the common wire on the motor. Secure it with plastic twist caps. Connect the black hot wire to the hot terminal of the speed controller. Use the instructions that come with the speed controller to identify speed terminals 1 through 4.
Connect speed terminal 1 to the low speed wire of the motor. Connect speed terminal 2 to the medium low speed wire of the motor. Connect speed terminal 3 to the medium high speed wire, and connect speed terminal 4 to the high speed wire of the motor. Cover any splices with plastic twist caps. Some motors have two high speed wires that are connected together by a capacitor. Only connect to one of the two high speed wires.
Turn the power back on and test the motor by turning it on and taking it through all four speeds.