I updated the "terminal diagram" ... it's still unclear, but I will do a better one later.
Notice that the cable colors may be different!
There's one thing I found in the TIS:
If you have manual seats without memory-function, then your car has the seat-heating-module.
That means, your seat heater is powered by the Junction Box with a pulse-width-modulation signal
If you have power seats with memory-function, then your car has the seat-module.
That means, this module regulates the seat heater on its own. Without Junction Box.
Still wondering what Pin 6 and Pin 7 are for ...