ENGINE BEGAN TO MAKE A "BUZZSAW" GRINDING SOUND THAT WAS NOT INITIALLY NOTICED WHILE DRIVING ALONG ON AN 85 MILE INTERSTATE HIGHWAY TRIP. WHILE TRAVELING AT 60 MPH ON A 6 LANE HIGHWAY, ALL THE DASHBOARD LIGHTING BEGAN TO DIM AND MALFUNCTION, THE ELECTRICAL SYSTEM THEN COMPLETELY FAILED AND SHUT DOWN CAUSING THE ENGINE TO STALL OUT, STEERING AND BRAKE FUNCTION BECAME SIGNIFICANTLY DEGRADED DUE TO ENGINE FAILURE (INCLUDING COMPLETE STOPPAGE OF THE WINDSHIELD WIPERS DURING A HEAVY RAIN DOWNPOUR) SAFELY EXITED ROADWAY BY MANEUVERING AROUND TRAFFIC AND COASTING TO ROAD SIDE SHOULDER AT WHICH POINT SMOKE STARTED POURING OUT FROM UNDER HOOD AND FILLING THE PASSENGER COMPARTMENT. CAR WAS SUBSEQUENTLY TOWED TO A MERCEDES DEALERSHIP WHERE THEY IDENTIFIED THE CAUSE OF THE FAILURE AND FIRE AS A SEVERELY DEGRADED ENGINE WIRING HARNESS. THE HARNESS WIRING INSULATION WAS FOUND TO BE BRITTLE, CRACKING AND FALLING APART, LEAVING INDIVIDUAL BARE COPPER WIRES TO MAKE CONTACT WITH EACH OTHER. THIS CONDITION CAUSED AN ELECTRICAL SHORT CIRCUIT WHICH STARTED THE WIRES BURNING, FORCED THE ENGINE STARTER TO BE CONTINUALLY ENGAGED WHICH IN TURN, AFTER 80+ MILES OF DRIVING, CAUSED THE BATTERY TO COMPLETELY DRAIN ULTIMATELY RESULTING IN FAILURE OF ENGINE AND ALL ELECTRICAL SYSTEMS. *TR