heres the B4 manual I have:
http://s2central.net/80TDi/Schematic...4/C-46-all.pdf
See the S12 fuse on page 7, 46/6 shows S12 only supplies the rev counter G5 and the reverse switch:
That page in Russian, cant read that mate,
BTW mine is an early 1z, no oem immobiliser at all, and no chip in the key. big plastic AFM. Diagnostic connectors are in the engine bay fusebox, 2 x single k-line connectors. Very early OBD implementation.