There are tons of threads on the final stage resistor issues, so you should search for the details. The short version is that the FSR is a part of the HVAC system and is located in the dash. The key symptom, aside from battery drain, is that, after the car sits for awhile, it runs the hvac fan continuously at a low level. You can usually hear it from outside the car if you are in an otherwise quiet environment. It can also give you unstable control of HVAC fan speed while driving the car.

Even if you can't hear the fan running, it is easy to pull out and check to see if it has any burn marks on it. Again, there are many threads with the exact details of troubleshooting and replacing the FSR. It should take maybe 20 minutes with simple tools to get it out.