DRIVING ON THE INTERSTATE APPROX 70 MPH FOR 150 MILES. THERE WAS A SMELL SIMILAR TO AN ELECTRICAL PROBLEM, NOTICED ACRID SMELL AND SMOKE OUT THE REAR VIEW MIRROR. PULLED OFF THE INTERSTATE. LOTS OF SMOKE FOR 5 MIN THEN STOPPED COMPLETELY IN 30 MIN. ALL LEVELS OK, NO LEAKS, NO FAILURES, ALL WIRING COOL, NO SHORTS, ALL INSTRUMENT OK. WAITED APPROX 45MIN THEN DROVE 150 MILES HOME WITH NO PROBLEMS. THE NEXT MORNING THE CAR CHECKED OUT OK. THE FIRE BURNED APPROX 18 INCHES OF INSULATION AND SCORCHED THE PASSENGERS FIREWALL IN SEVERAL PLACES. WHY DID THIS HAPPEN? *TR