Yup, what year is your truck?
I think blower fan resistors were only used on 3rd gen and newer (1990+).
I know for sure that 1st gens do not have resistors, and Bevins '85 also does not have one.
Also, a simple way to check if your heater core is plugged or not, is after your engine has warmed up, move your climate lever to full hot, and with the engine idling, open the hood and compare the temperature of the two heater core hoses that are located above the back of the cylinder head, and plug into the firewall. The two hoses will be about 200 degrees, and should both be nearly the same temperature, plus or minus like 5 degrees...
Mike
