One problem related to air bag on-off switch has been reported for the 1998 Audi A4. The most recently reported issues are listed below.
Passenger's airbag deployed upon impact. No passenger or parcel on passenger's seat, drivers bag did not deploy. Audi continues to deny a problem existed. Audi's own documentation describes a no passenger lock out switch to prevent deployment of the passenger's airbag when no passenger or (heavy parcel?) is present. I was the only occupant in the car, had my seat belt buckled, pretensioner for my seat belt fired but my airbag did not deploy. An interlock, by definition, is either on or off. An interlock or lock out device does not act as a "maybe on" or "maybe off" gate.