Aside from making certain that you also have GND connected to the LED, I would try connecting the motor to a serial port on a PC and using HyperTerminal to verify the communications work with what settings you believe the motor is configured with.
I’m not sure you need the level shifter for motor to LED connection since you motor is using 5VDC.
You may need the level shifter for connection to the PC since the PC likely uses somewhat standard +/- 13VDC or so.
RS232 levels can vary from +/- 3VDC to +/-25VDC.
I have not used a level shifter but your description of the connections seems correct.