I don't normally like to guess at things but it could be for the TD box, cruise control box, or an option like the Super Monitor. As I recall all are located in that area.
Nick: You be welcome. As they say, each of us knows something...together we know it all. I'm not familiar with the Supra's airbag system but I can tell you from other systems I've worked on the accelerometers used for bag deployment are sophisticated gadgets and not usually mounted in such a place.