I used to have an Orion 16i Ghia years ago and exact same thing happened. There is a bracket type thing which gives support to the dash and there are about half dozen wires that run past it. If you have been fitting a new stereo or have disturbed them slightly they may have been rubbing on this bracket and caused the short. That's what happened to me I lost headlamps as well although my side lights would work. Burnt all the insulation back for miles. Had to repace all the burnt wiring.

Good Luck mate

SMG