1989 Dodge Dakota 3.9L, heater/ac blower motor (fan speeds) resistor block.
If you are having trouble with your heater/ac blower (not working or only working on certain speeds) you might want to look at the resistor block (or the wiring harness) that controls the blower speed before pulling it. You can read the DodgeDakota.com discussion on this topic here: http://www.dodgedakotas.com/boards/dea/62.html
For what it is worth, the resistor block is not shown in the Haynes Dodge Dakota Pickup 1987-96 manual wiring diagram. Here is a better wiring diagram (more model year diagrams can be found here):
The resistor block on my 1989 Dakota is located on the passenger side firewall (see yellow arrow).
The block or board (there are different types) maybe located under the dash in certain year models. There is an excellent page about this here.
The plug simply pulls off. Remove the the two screws (I used a 5/16" nut driver) and .....
...the unit pulls right out.
Speaking of the screws; they are not completely threaded and the shaft is slightly undercut compared to the threads. It is possible to turn them in so far that they will turn freely (feeling like they are stripped). If this is the case; apply a little pressure on the block (pushing/pulling it away from the firewall) and they should screw out. I would recommend some small washers under the screw heads when you reinstall the unit. I didn't have any handy, but a turn of wire on each shank works fine for now.
One of the resistive wires on my unit had burnt apart (causing the unit to be totally inoperative). The blue line represents how it would have been attached. It is also possible that you might have a bad connector or wires (as reported on various forums).
To repair it, I simply moved the remaining wire to the next slot (red arrow). It works fine.
The cutoff terminals (bottom right of the photo) were like that when I removed the plug.
A new box is in the $10 - $15 range from a Dodge dealer. http://www.rockauto.com has them for $7.22 + s/h; the part number is RU95.
Clean up and reinstall.