What was found
WHEN SETTING UP FOR A LANDING APPROACH, THE PILOT NOTED THAT THE LG CB HAD POPPED & FURTHER NOTED THAT THERE WERE NO GREEN DOWN LIGHTS ILLUMINATED. THE PILOT PERFORMED AN EMER GEAR EXTENSION & DID A TOWER FLY BY TO VERIFY THE GEAR APPEARED TO BE DOWN. THE LANDING WAS UNEVENTFUL. TROUBLESHOOTING DISCLOSED THE DIODE BOARD PN 584-427 WITH BURNT & DESTROYED TRACES. INSTALLED NEW DIODE BOARD & CYCLED THE GEAR SEVERAL TIMES IN THE SHOP WITH NO OTHER ISSUES NOTED. RETURNED ACFT TO SERVICE. PILOT TAXIED OUT FOR TAKEOFF & DURING RUN UP NOTED THAT THE GREEN GEAR DOWN LIGHTS WENT OUT & THE PUMP CB POPPED AGAIN. RETURNED ACFT TO SHOP & BEGAN FURTHER TROUBLESHOOTING. FOUND NEW DIODE BOARD WITH IDENTICAL DAMAGE AS THE BOARD IT REPLACED. SUSPECTED AN INTERMITTENT SHORT TO GND IN ONE OF THE WIRES TO & FROM THE GEAR DOWN MICRO SWITCHES. FOUND NO ISSUES WITH THE SWITCHES ON THE MAIN GEAR BUT AFTER REMOVING COWLING, FOUND TWO WIRES THAT WERE BURNED & CONTAINED BARE WIRING INTERMITTENTLY SHORTING TO GND ON THE EXHAUST CROSS OVER TUBE. WIRE NR D13B20 & G1H20, WHICH GOES TO CONNECTOR J410 ON THE NOSE GEAR DOWN LOCK SWITCH. REPAIRED BOTH WIRES BY SPLICING IN NEW SECTIONS OF WIRE. ROUTED & SECURED WIRE BUNDLE AWAY FROM EXHAUST CROSS OVER TUBE & INSTALLED ANOTHER NEW DIODE BOARD. CYCLED GEAR SEVERAL TIMES IN SHOP & TEST FLEW ACFT WITH GEAR OPERATION NORMAL.