I have a salvaged Model S. I have a warning on the dash that the heater is not available. The service center did a few things on my car before telling me they were not going to provide any support for my car as the title is not clean. The service tech did tell me that he thought it may just be a bad PTC Heater, so I replaced the PTC Heater. I have already replaced the two fuses in the junction box. I had the firmware redeployed and it hangs up on the PTC Heater and will not go any further. Meaning, the car is not communicating with the PTC Heater. I am not good at electrical fault tracing. What are my next steps to diagnosing this issue?