Diagnostic connector "B" under the bonnet is where you read the codes Luke, as for your mate that kept spinning the steering wheel, in future cable tie his hands behind his back before letting him near the car!
According to Volvo, any more than 3 turns in either direction will kill the rotary coupler/clock spring/contact reel/squib so it's a fair bet your mate murdered the original.
Are you sure the one you gave your mate that owns the car is ok? Could simply be it's held and recorded the fault from the first one that died so the replacement might be fine but you need to clear the fault first using the diagnostic connector.
I can't find any evidence that the SRS ECU has power from fuse #1, as it's (supposedly) a safety critical item it's possible it has its own internal memory in the SRS ECU that needs clearing - i know of a few other cars like that. Good call pulling fuse #1 to try and clear the memory though!
