Mission accomplished.
5 wires (B+) were connected in a pigtail, which was very corroded (the green dusty stuff). I touched the pigtail and all wires just fell off from it.
I stripped them, joined them together and pigtailed them again, this time I used a special crimp from my toolbox.

Central locking system works like a charm now.

I had to remove the passenger's side seat and lift the carpet. I took some pictures which will be posted soon.

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1999 Porsche 996 Carrera Convertible
1994 420E - SOLD
1986 300E - SOLD, what a car
609 Certified