OK, so i've managed to get hold of a more colourful and in-depth diagram of the right seat (old model) Which i've attached below. I've removed the diagram from the illumnation circuit going to ILL+ as that diagram is a another big diagram itself related to relays that turn the backlight on. And also i've left out the bottom connections on the heater switch as those connections are related to cooling seats where there is a fan activated by another circuit and that all works fine. So for the purpose of trying to figure out how the heated seats are working on this, you can see that the main heater switch (which is a switch with a dial between 1 to 3 setting for temperature) sends two wires to the heater control (black box). The heater control black box has it's own 15A fuse and earth connection which it uses to heat the heating element when the correct signal is received from the switch. Now the question is, i've figured out that the wire that goes from the heater switch to what is called THL/THR (L for Left and R for Right) gives a varying voltage between 10 and 12v which lets the black box determine how hot to make the heating element. So unless there is a voltage coming to TH the heating element isn't activated.
What I don't understand is what role the SW connection makes to the black box. Because according to the diagnostics document SW is supposed to give a voltage of 12v when heater switch is turned on regardless of what the temperature dial is set to. So TH gives a voltage range between 10 and 12v depending on heat setting and at the same time SW gives 12V. So essentially the two work together. However, when i did the bench test by connecting a bulb to the output, i was able to make the bulb light up just by providing the 10-12v on the TH line.
