I have a 2013 fiesta and have been using it for uberEATS driving. I have had the back rest seat spring fail on me and I have replaced it last year. The new just broke. I got a replacement(s) (both seats cost the same as 1) from a junkyard from a 2017 fiesta. The cushions are much better and I want to keep using it. The plugins were different for the driver seat so I used the old wiring harness (the plug in where it plugs into the car is different, but the plugins to the harness under the seat were all the same so I used the old harness and that worked). The car knows if I am buckled up (so some info is transmitted), but the airbag light on the dash is lit. Through trouble shooting I have found both new seats are the problem even when plugged in (passenger seat knows when passenger is sitting in it). The new seats feel so much better and I don't want to give them up (and sunk cost fallacy). 

Side note (after I got the seats in the car I found one of the hooks was broken in the same spot. Used a zip tie and It seems to be holding. this will be my fix for this issue from now on for whatever seat I use)

 

• My question is, can I remove the airbags from the old seat and put them on the new seats, or would that damage the airbags making them unusable? 
• Can I remove the cushions entirely from the new seat and place them on the old 2013 frame?
• If I ignore the airbag light and get into a crash, what airbags if any will deploy? I live in America and as my driving instructor told me "the vehicle with more lug nuts wins". I'd rather not become a statistic caused by the compensation from my countrymen.
• Do the new seats work and I just need something or someone to clear it? A base OBD2 reader isn't reading any codes.
• Did I damage the wires by accident when I tried to remove the seats from the junkyard car without disconnecting the wires?

Figured it out. You can swap the airbags without damaging them.