firstly do not mess around with the airbag system with test lights or testers on any of the electrics you will get a big surprise.
Leave the ignition off for at least 2 mins.Look under the seats for a yellow plug.if the plug has not come apart,unplugg them and reconnect them.if this does not cure the fault get it code read to point you in the right direction.There is a softwre issue on some of these and you may find a dealer will do an upgrade.