Don't know where you got your info . The heater blower motor electrical B+ power comes from Fuse F 64 a 40 amp fuse . This goes right to the blower motor on the green with orange stripe wire , The black with red stripe wire goes to the switch for high speed . There is Splice 24 that ties into the black with red stripe wire. The splice 24 turns into a black with orange stripe wire . An this wire goes to the blower motor resistor . All the switch does is route the B+ voltage through the different resistors to ground .
Thermal resistor "usually" stops working is because of faulty fan speed switch ???? Totally not true , resistor assemblies fail because of the heat associated with dropping voltage across the resistors , That is why they put the resistor assembly in the air box . Air blows over to cool the resistors . The switch is nothing more then a way to direct different speeds to ground .
Rather then listening to other people ,why not learn the right way to test electrical circuits .
Electric Testing Techniques You Need to Know
Do you know what a wiring diagram is ?
http://www.bbbind.com/free_tsb.html Enter vehicle info . Under system click on HVAC , under subsystem click on heater . Click the search button , then on the link . Use a volt meter an test , don't guess !