What was found
A/C ARRIVED AT SHOP AFTER EXPERIENCING SMOKE IN THE CABIN. ELEC SYS WAS SHUT OFF (MASTER SWITCH). INSPECTION OF ELEC SYS SHOWED EVIDENCE OF A FIRE INSIDE OF VOLTAGE REG. VOLTAGE REG WAS INSTALLED IAW INSTRUCTION SHEET NR PPS-2020. THE VOLTAGE REGULATORS INTERNAL OVER VOLTAGE RELAY FAILED. THIS RESULTED IN AN (OVER VOLTAGE CONDITION). FOUND MULTIPLE ELEC UNITS (BLOWN) FROM LND LTS, FUEL QUANTITY GAUGES, BEACON FLASHER AND LAMP, TO ALL RADIOS. THE ORIGINAL OVER VOLTAGE RELAY (FROM MFG) IS DISCONNECTED W/ OTHER UNIT INSTALLATION IAW ABOVE INSTRUCTIONS.