After-market Central locking would be the most probable cause for it. Installers have habit of running wires directly to Central locking unit without putting proper fuses in place and using cheap wires whose insulation gets cracked on its own with time. (Insist on using Finolex, L&T, Havvels etc wires) Rats are another cause for short circuits, they chew wires insulation. Chewed ABS wires once in my car and once got inside car after cutting insulation around AC air circulation vent. Ask your friend to insist on getting the root cause of fire found out by Fiat.