I hesitate to suggest much in this area as I do not have an 89 FSM, but a scan of my 1990 FSM suggests checking the control module red/black (2B) input wire for full battery voltage. It is fed by a fusible link which is hot at all times. I don't find a specified output voltage for high speed in the FSM, but there is an orange feedback connection between the purple blower motor wire and terminal "P" of the programmer which is under the right side of the dash. I would guess that is where the programmer determines if commanded voltage is equal to actual voltage. It also says the command from the programmer to the blower module is a variable voltage.
I do not know if there is a blower fan override or output control in the BCM diagnostics or not. Some functionality is different between the touch screen cars and the non. The BCM is the master controller here.
In my FSM, only two conditions have a diagnostic tree: high speed fan only, or no fan operation at all 😖