What was found
CREW REPORTED, ON DESCENT, NOTICED AN ODOR AND SAW SMOKE COMING FROM CABIN HEAT SWITCH. EMERGENCY WAS DECLARED, DEACTIVATED ALL ELECTRICAL SYS AND SMOKE STOPPED. TURNED ON SELECTIVE ELECTRICAL EQUIPMENT ON TO FINISH APPROACH, LANDING WAS UNEVENTFUL. MX FOUND CABIN HEAT SWITCH SHORTED. R & R SWITCH, SYS CHECKS OK. ACFT RELEASED BACK TO SERVICE.