JW, I think I wasn't clear enough and you have misunderstood me. I'll try to explain it again with pictures.
Below is the pic of the PTC heater and the 4 cables that come from it. I've already wired myself the wiring for the big cable. My question is for the other two cables ( thin ones, black and brown, the ones on the right side below). My car doesn't have the socket to connect/plug them. Do you know how I have to make the connection in that occasion? I hope you understand me now. Thank you in advance for your cooperation. I am looking forward to hear from you. Cheers.