TRAVELLING NORTH ON I25 IN NEW MEXICO. GOING 60 MPH PULLING A 5TH WHEEL TRAILER. LOW FUEL PRESSURE LIGHT CAME ON AND LOST POWER STEERING. SMOKE COMING FROM UNDER HOOD. THEN ALL WARNING LIGHTS CAME ON AND COASTED TO SIDE OF THE ROAD. BY THE TIME I STOPPED, THE ENGINE COMPARTMENT WAS FULLY ENGULFED IN FLAMES. TRIED TO RELEASE THE HOOD BUT CABLE MELTED. EXITED THE VEHICLE AND CALLED 911. PASSER BY LOANED ME FIRE EXTINGUISHERS BUT FIRE TOO HOT. FIRE DEPARTMENT ARRIVED WITHIN MINUTES AND EXTINGUISHED THE FLAMES. TRUCK TOWED TO A HOLDING YARD.