This happend a few times to my tf sometime back...srs light stayed on when engines started....it eventually cured itself .disconnect the battery and leave for a 10 minutes before attempting to work on the srs...the first place to try would be the underseat connectors...maybe the car is damp with the recent weather...another place to check is damage/wear to the rotary coupler...you may read all about the srs system in the workshop manual available to download off this forum
It's always a good idea to own a obd2 scanner..mine is the torque ap on android....
There is a large section on srs in the manual..heres another extract.