electrical fault error

After buying the car 2 months ago with the Offside headlight not working, I though - "not a problem, should be able to sort that myself". How wrong I was! - Initial investigation by garage traced it to the Ballast unit, which I sourced new unit on ebay (£140) plus all the investigation...

Help After recent spirited driving session, noticed airbag light, CEL and error on main display. Once I was home noticed in addition; rear indicators not working (hazards + interior indicators okay) rear lights not working electric seats not working front sidelights not working Everything...