madd, when you get your new heater blower motor resistor installed, first be sure all the leaves and crud are cleaned out of the heater box and install a screen over the inlet to the box. Make sure the resistor is standing well proud of the heater box and that there is no crud for it to start on fire. Then run the heater for a good long while in all three switch positions (high, med and low) and feel all the wires going to the blower and resistor. Don't touch the resistor because it may be very hot. (The resistor will get hottest in the "low' position, where it is providing the most voltage drop, while the wiring will get hottest in the "high" position, where the blower is drawing the most current.)
If you feel any part of the wires or connections (except the resistor itself) getting really hot, repair the high-resistance point that is causing it before you button up the dash. Usually the high resistance point is at a connection, such as a spade lug.
Get some high-quality spade lugs and solder them to the wires if you have to replace any. Hot wires like this can lead to an under-dash fire, fanned by the blower, which can easily burn the entire car up unless it is put out immediately. Such fires were fairly common on these cars. This happened on my '78 dually when it had 22K miles, when the P.O. was pulling his fifth-wheel trailer. I replaced all the burned wires with larger gauges, soldered the connections and used high-quality spade lugs and it has been fine ever since. Also, carry a fire extinguisher.
