What was found
PILOT REPORTED ERRATIC FUEL FLOW INDICATION. DURING GROUND ENG RUN-UP FOR T/S, A LOUD POP WAS HEARD, LARGE SPARK SHOT FROM BEHIND COPILOT'S INSTRUMENT PANEL, AND THE 3-AMP STEREO CB OPENED. INVEST REVEALED THE 28-VOLT POWER LEAD FOR THE STEREO (INSTALLED SEVERAL YEARS AGO) HAD BEEN CHAFING AGAINST P/N 1200106-263 ALUMINUM LINE (DECK PRESS REF LINE FROM AFT SIDE OF FIREWALL TO FUEL FLOW/MAP GAUGE). CHAFING HAD PROGRESSED TO THE POINT WHERE INSULATION HAD WORN AWAY EXPOSING CONDUCTOR WHICH HAD SHORTED AGAINST THE LINE AND ARCING HAD EATEN A .0625 INCH DIA HOLE IN THE LINE. SINCE THIS IS TURBOCHARGED INSTALL, LEAK IN THE DECK PRESS LINE RESULTED IN FUEL FLOW READING EXCESSIVELY HIGH AT HIGH POWER SETTINGS.