AROUND 6 MONTHS AGO A PLUME OF THICK BLACK SMOKE EXITED THE ENGINE COMPARTMENT. I INSPECTED THE ENGINE BUT COULD NOT LOCATE THE SOURCE AND FIGURED IT MIGHT HAVE BEEN SOMETHING FALLING ON THE EXHAUST SYSTEM. RECENTLY I DISCOVERED MELTED AND CORRODED WIRES LEADING TO THE FUEL PREHEATER. NO FUSE WAS BLOWN. I HAVE NOT TAKEN THIS VEHICLE IN FOR REPAIR YET, SO THE COST ESTIMATE IS SIMPLY A GUESS. IF A SHORT EXISTED IN THE PREHEATER, THEN THE FUSE SHOULD HAVE BLOWN. EITHER THE FUSE IS TO LARGE, OR THE WIRE SIZE IS TOO SMALL FOR THE APPLICATION.*AK