The fuel cut-off switch is in the trunk, sitting in the driver's side rear panel and covered with a rubber boot. It's a small switch kind of hard to reach. As far as I know, the fuel cut off light should be showing to let you know it's been tripped.
I would recommend getting a Probe Service manual for your year of car if you plan on replacing the airbag yourself. Theres certain steps that it lists out. These manuals are not real easy to come about since they were made for Ford Service depts...
I'd get the manual. Also, has the rest of tyhe car been professionally repaired? Most airbag systems are often operated by physical sensors in the fender area that are pushed in when an accident occurs and tells tha bag to deploy. If this isn't fixed, a new airbag could potentially deploy.
Airbags can certainly be dangerous.... I think this is an area that I would leave to professionals.