bmwman528e
OEM system is safer then retrofit:
It shuts down when thermistor is too hot or disconnected,
It regulates heating by using thermistor signal VS klixon in majority of retrofits;
Most of all it looks better. It is much easier to install then retrofit. Extra cost is $100-$150 (OEM switches and connectors). It is approximately 15 minutes to install OEM switches in the center console and relay in the trunk.

nigwhyrito: I repeated test that was described in post #25 and found that threshold is 4.5kOm for LOW (one LED on) and 3.5kOm for HIGH (two LED).

I selected 10kOm thermistor from DigiKey. It regulates heaters at 100F (LOW) and 110F HIGH. My heating pads (Carbon mesh from EBay) have build in klixons set for 140F.

nigwhyrito:I think your 100kOm thermistor will not regulate. Your heater is regulated by klixon (thermal protection switch). It is good to keep klixon for protection and not to use continuously. Klixons do fail and then heater will be running continuously without regulation.