We had similar problem with our Peugeot 207 but was found to be a faulty wiring connection under the driving seat which had become dislodged due to something having been stowed under the seat.Local dealer sorted the problem quickly.If there is no evidence of a wiring problem I suggest you get a Ford dealer to resolve this asap as you cannot afford to risk driving with what may be a faulty air bag system.
Roger
December 2007