Finally getting back to this project... because it's "cold" in Los Angeles, haha. Did you ever finish this? Looking at one of your other posts I see you drive a Golf TDI. I drive a Golf TDI S. I currently have seats in my car (from a GTD, imported) that have heating elements and I also have a retrofit harness from Kufatec that I need to install. I was/am under the impression I need the highline BCM as well.
My installed BCM is 5Q0937087Q. Had the dealer look up the replacement in ETKA and it is 5Q0937087S. ETKA shows the 5Q0937087S as the replacement for -Q and -R BCMs. You need pins A2, A5, C40, C43 and C56 for the retrofit, according to the instructions Kufatec provided with the harness I bought from them. I have pictures of my BCM, but only plug B. For some reason I, like you, was thinking I needed B43 which my -Q BCM does not have. I need to check for all the required pins on my BCM. I would love to put $350ish a new BCM will cost me into something else, like a CR190.
Did you buy the 5Q0937087S to do this retrofit? And does your 5Q0937087S have pins A2, A5, C40, C43 and C56? If so you should be good to go.
Edit: My memory is failing, I did in fact take pictures of all plugs on the BCM and I am missing the required pins on connector C. That's probably why I have these ETKA printouts showing I need to buy the -S BCM.