[JCz04Bimmer]

So! I'm almost there.

It turns out that pre-2004 (I think) Z4's (of all types) used a sensor mat that is different from the one used in post-2004 Z4's. The pre-2004 mat uses an external control box of sorts with p/n 65778367242. The post-2004 Z4's mat has that control box integrated into the mat itself. However, the wire that ultimately connects to the yellow harness attached to the seatbelt buckle apparatus has the same pins in the same location with the same colored wires.

So, if you use a sensor mat from a pre-2004 Z4 you'll need to make sure that you also either have (or buy) a small wire with p/n 52108240500. The sticker on the wire has the number "8240500" on it. This is the wire that connects from the small control box to the wiring harness attached the seatbelt buckle apparatus. I'm going to be connecting everything up this weekend and will do a reset and, hopefully, that pesky red airbag light will be gone for good! Stay tuned for an update at the end of the weekend!