1972 York Furnace wiring to a blower motor
The wiring diagram is printed on the side of the motor.

Brown, Brown/White
The Brown and Brown with White wires go to the run capacitor. If the old motor did not have a capacitor, you'll need to get a 10 microfarad 370 VAC capacitor. Mount the capacitor, and connect these wires to it.
Yellow
The yellow wire is one of the line wires. It will either go to L2 or neutral, depending on the motor and the system it is installed in.
Black, Blue, Red
These wires are the speed taps. You'll connect one of them to power at a time, to make the motor spin at the desired speed. Black is high, Blue is medium, and Red is low speed. In some furnaces/air handlers, you'll simply park each tap at the corresponding terminal on the fan control module.
Rotation Direction
This motor also allows you to select the rotation direction, by simply connecting four wires in the appropriate configuration.