As a follow up on this - there are four (4) weight sensors from what I understand, one at each corner near the mounting bolts where the seat mounts to the floor. If you removed the seat and reinstall it, the torque on those sensors can change, causing a negative weight to be registered by the airbag system. The seat has to be recalibrated to zero like a shipping or bathroom scale to correct the error. When you sit in it, the sensor 'sees' a positive weight and all the lights go out.
Or, if you are lucky, you can uninstall the seat and reinstall it a second time like I did, changing the torque on the bolts again, hopefully resetting everything back to normal (worked for me - maybe I should play the lottery).
If the light came on without uninstalling the seats, you might have a bad sensor or one is unplugged. See if you have something stuck under the seat near the mounts.....