My question is, why are there spliced wires?
To me that says that the car was in a previous accident with airbag deployment. Bearing that in mind, I don't doubt that the reconstruction of the car wasn't fully completed. Or, as in the case of the seat, it was done with salvage parts that don't communicate well with the parts that are supposed to be in the car,,, as in they pulled parts form another Focus with SRS and not the specific part numbers that belong in your car.
This may be a argues process but, what I would do is go through and write down the part numbers you find and check them against what Ford says should be in the car. It's probably best to go to Ford parts in person with the list. That way they can tell you is a part # has been superseded or renumbered.
IMO, verifying the correct parts are there is step #1.
Don't "think outside the box".
There is no box.
Do it correct, or do it twice.