if the old seats did not have airbags where as the new seats do then the connector that used to plug into the old seats can't be for the airbag, can it..........
your trying to plug the wrong things together. I believe the old style passenger seats had a sensor on the base that allowed the car to know when the passenger seat was occupied, so it knew when to figre the passenger dash airbag or not. no point in blowing an airbag if there is no one there to hit it after all.
now are you sure its the passenger airbag light that is on or is it the airbag light itself? there should be the option to turn the passenger dash airbag off, in the door jam for the passenger door on the end of the dash, for if you have baby chair installed etc.
you would need to hot wire the connector somehow so it always thinks someone is in the seat but be very very very careful when playing with airbag systems as you can either cost yourself or someone you love their life in an accident if you get it wrong, or you could potentially detonate all the airbags the next time you turn the ignition on, neither of which is cool.
chances are you will not get the airbags in the seat to work as you're probably looking at having the older MY97 airbag system where as the system with all the airbags were MY99.
biggest question is what colour is the light you have on. I think the passenger warning one is amber which is okay where as red means its an error and the entire airbag system is offline.