It's easy to find and a super easy replacement if you own and can work a screwdriver. The module is located on the underside of the dash on the passenger side. visible only from below. It's about 1" by 4", it will have a 5-wire harness attached that you may be able to follow to the blower motor (the round bulge on the far right), and is held in by 2 screws. To remove or replace it, disconnect the wire harness, remove the 2 screws and pull out the module. Installation is the reverse process.
Under the dash, far passenger side.
Diagram for location of blower motor resistor can be found herehttp://autorepair.about.com/library/images/bl441a-lib.htm
Your truck has both. the resistor is between the switch & blower.thje resistor controls the blower speed
For the 1989 Dodge Ram, the heater blower motor resistor can be found on the passenger's side, on the bottom of the heater box. It is beside the blower motor.
check the blower motor resistor pack. should be firewall side of heater rectangular connector with 4 or 5 wires.
Blower motor is under the dash on the passenger side.
Under the dash on the passenger side in front of the blower motor. You will see 5 wires going into a plug held in by 2 screws. That is the blower motor resistor.
I belive it is located down under the dash on the passenger side. the older dakotas where mounted on the passenger side of the fire wall. a blower motor resister is usually located close to the actual blower motor.
Under the dash below glove box. You will see the blower motor and it's to the left of it. You will see a wire harness going to it.
replace the blower motor switch
Could be a bad blower motor, or, look to the blower motor resistor mounted on the engine firewall on the passenger side near the top of the firewall inside the engine compartment. It will have five wires going to it. It is likely either burnt out, or the wires have shorted at or near the resistor.
The resistor block or blower motor resistor is used to control the speed of the blower motor. That is how you get the lower speeds on your air conditioning or heater. The higher the resistance the lower the speed of the motor.