Not the usual resetting issue! Instrument panel on my wife's Barchetta died on her last week. Traced problem to loose contact on back of fuse panel so all fixed there BUT airbag warning light stays on. Diagnostic check comes up with 'airbag isolation switch warning lamp fault'. Replaced bulb and checked all contacts again but no joy. Isolation switch itself seems fine but warning lamp doesn't light up and error message obviously being sent to ECU.
My guess is a wiring issue but where to start looking? Also a bit scared of setting off other problems with airbag system.
Any advice or pointers would be much appreciated. Thanks.

I had the instrument panel out, and managed somehow to trigger the airbag light. I could be wrong but I think having the ignition on without the airbag light connected can trigger a fault code and the light...I don't think the airbag light will extinguish if the fault is removed, only by clearing the codes in the airbag module. Mine all cleared ok using a cheap kkl diagnosis cable and the free version of multiecuscan, but from what I've read it can depend on the type of airbag ecu fitted.

Other posts regarding airbag warning light say that the plug connector under the seats can de an issue, as in dirty contact.

Reading the op again, it sounds like the ecu thinks the bulb which flashes orange to say the passenger airbag is on, has blown. If it doesn't flash (or stay on continuously when passenger airbag disabled), it would still point to the bulb, or perhaps one of the connectors at the back of the instruments? Try and trace to one of the contacts, it could just needed cleaning up (and then the fault clearing)

Thanks to all for the advice. Have had the instrument panel out again, checked all contacts and tested the relevant bulbs. Still no sign of life from the isolation switch warning light but airbag light itself still on. Tried it with bulb removed but seatbelt warning light then flashes continuously which is even more annoying! Does anyone know which colour wire feeds the offending bulb so I can check that this is intact? Am reluctant to start probing about with voltmeter in view of warnings in other posts on airbag issues.