What was found
(CAN) WHEN PILOT SELECTED GEAR DOWN AIRCRAFT EXPERIENCED MULTIPLE FAILURES OF MLG & FLT INSTRUMENTS, ALSO THERE WAS SMOKE IN COCKPIT. PILOT EXTENDED THE MLG MANUALLY & LANDED W/O INCIDENT. MAINT DISCOVERED 2 PROBLEMS: THE WIRE GOING TO BUS FEEDER DIODE WAS NOT PROPERLY CRIMPED & BECAME LOOSE. SOME ARCING OCCURED WHEN WIRE BECAME LOOSE & CAUSED SMOKE. THE CONNECTOR AT ENGINE INSTRUMENT C/B PANEL HAD BECOME CORROADED BECAUSE OF WATER COMING IN SIDE PANEL & NOT ALLOWED CURRENT GO THROUGH IT, THIS CAUSED MLG & FLIGHT INSTRUMENTS TO FAIL.