What was found
(CAN) DURING APPROACH FLIGHT ON MULTIPLE OCCASIONS THE PILOTS EHSI FAILED ON APPROACH , POWERED DOWN AND RE POWERED UNCOMMANDED. ON EACH OCCASION THE SYSTEM TESTED NORMAL AFTER LANDING AND DID NOT REOCCUR FOR DAYS. EACH COMPONENT IN THIS SYSTEM WAS REPLACED WITH A SERVICEABLE UNIT WITH NO CHANGE. DURING INSP OF THE A/C WIRING CHAFED WIRING WAS DISCOVERED UNDER THE COPILOTS SEAT IN THE OUTFLOW VALVE COMPARTMENT.