Wrong Seats Leading To Airbag Warning Light?

Hi all. I've had a look around and can't find what I'm looking for so hope you don't mind me asking this.

Basically I have a 51 plate Mondeo tddi estate ex taxi thing with the airbag warning light on. I've had the codes read by two different garages who have told me there are 3 fault codes pertaining to the passenger seat (no more information than that) they have then followed this with blank stares and mumbling when I asked "so what do I need to do?" Which isn't particularly helpful.

Anyways I've spoken to a few more people who believe my front seats aren't original and are from a later mondeo with different wiring bits and bobs. I've looked at the underwear block and to my layman's eyes nothing seems amiss. There are two plugs in the back of the block (and 5 or so empty sockets), one orange from the seat belt buckle stalk, I presume for the pretensioner release, the other yellow plug is from inside the seat, presumably from the occupancy sensor. Nothing else is in the back of the block, then many wires come from the front of the block. Nothing looks bodged, loose or recrimped or anything. Are slightly later seats likely to have wildly different wiring if all the plugs fit in fine?

Any idea what I should do?