2003 Volvo V70 short circuit

Just bought v70 been on long run-occasional problem of misfire in the form of a big jolt in performance followed by red triangle showing in display, REAR PASSENGER DOOR OPEN, as time has gone on the fault turned into SRS AIRBAG SERVICE URGENTLY REQUIRED followed with yellow warning triangle, then developed into all electric failure with a crackling sound from behind dash on right hand side of steering wheel had to stop and re-start to erase problem, occasional display of STOP SAFELY BRAKE FAILURE all in all this appears to be some form of electrical connection causing fault, I will take to garage to get diagnostic however a clue as to what to expect would be helpful, biggest fear is have I bought a duffer ?