On July 2, 1993, at approximately 1815 Pacific daylight time (PDT), a Cessna 414A, N4735A, experienced a main gear collapse while landing at King County International Airport/Boeing Field, Seattle, Washington. The FAA certificated airline transport pilot, who was the sole occupant of the aircraft, was not injured, but the aircraft sustained substantial damage. The flight, which departed Winthrop, Washington about 1710 PDT, was operating in visual meteorological conditions at the time of the accident. The aircraft was on an IFR flight plan, and there was no report of an ELT activation. According to the pilot, while preparing to land at Winthrop, the green gear-down light for the right main gear did not illuminate after he put the gear handle in the down position. He then cycled the gear five times, and checked the bulb itself to make sure it was good, but still did not get a green gear-down light. He then used the emergency extension system to "blow" the gear down, after which the right main gear-down light illuminated. After having someone on the ground check the gear position during a low pass, he landed with no further incident. After making a ground check of the aircraft, the pilot departed Winthrop en route to Seattle. The pilot said that during the takeoff, the gear-light holder fell out of the panel and ended up on the cabin floor. He said he did not raise the gear, and after getting the aircraft stabilized at cruise, he put the holder back in position. According to the pilot, as he was putting the holder back into position, the lights flickered and went out, followed by the loss of a number of other electrical components. He then continued on to Boeing Field and executed a normal landing. After touchdown, at a speed of about 60 to 70 knots, the right main gear collapsed. According the FAA Inspector who responded to the accident, the pilot did not attempt to contact his company maintenance personal while on the ground at Winthrop, nor did he lock the gear in the down position with an external mechanical lock prior to departure from Winthrop. Inspection of the internal down-lock mechanism showed scoring and corrosion of the metal in the area where the down-lock teeth are meant to slide into the engaged position.