Ok, borrowing Ofer's harness plug pic, I took off the cover on the manual seat plug to see what goes where. So I marked it up as to what's in the manual seat plug. Interestingly, there's one pin that the new harness doesn't have, and it's blue. The same exact color as the two blue wires going to the mystery airbag switch. Problem is, there's a blue one right next to it. Is this the other color to the seat belt switch which has the same color blue and an orange one? Perhaps this missing pin is the missing link?
I'm probably going to dissect the tape and conduit on the old harness to see exactly how that switch is wired in. But likely tomorrow. I'm too tired to worry about it tonight.