CAPE CANAVERAL, Fla. — Spacewalking astronauts triumphed over a stubborn bolt and installed a critical power-switching box at the International Space Station on Wednesday, reviving electrical systems.

‘‘Looks like you fixed the station,’’ Mission Control told the crew on the radio. The problem had cut the amount of electrical power available to the orbiting lab, and a variety of equipment had to be turned off.

Engineers on the ground and the astronauts in orbit scrambled over the Labor Day weekend to devise makeshift tools to clean metal shavings from the socket of the troublesome bolt, after last week’s failed effort to plug in the new power-relay unit.

This time, NASA’s Sunita Williams and Japan’s Akihiko Hoshide were armed with a blue toothbrush, a wire brush, and other jury-rigged tools.

The two applied grease to the sticky bolt and blew away most if not all the metal shavings, debris that was discovered during last Thursday’s eight-hour spacewalk, one of the longest on record.