I always found that the time that the heated seats stayed on high was too short. By changing the value of two resistors the time can be increased from 4 minutes to 11 which I find perfect.
Look for two 84500 ohm resistors (gray,yellow,green,red,brown). By changing these to 200K ohm, the time increases to 11 minutes.
These details apply only to the 126 820 18 26 heated seat control module (used in 124, 126 and others) but other modules can probably be modified as well.
Next step is to add a thermistor so the time varies with vehicle temperature (maybe next winter).