As governor of New York, Andrew M. Cuomo has no shortage of complex problems demanding his attention. But his ire has recently been focused on a small switch in a subway station deep below the streets of Manhattan.

Delays with the switch, known as a shunt trip breaker, were holding up progress on the Second Avenue subway — a “demonic device that has frustrated us for months,” Mr. Cuomo said as he inspected a new station at 96th Street on the Upper East Side on Monday.

“There’s 800 little things like shunt trip breakers that you have to get past,” the governor said. “Each station has its own little problems.”

The notorious Second Avenue subway, nearly a century in the making, is inches from the finish line, and Mr. Cuomo, a Democrat, has made it his mission to complete the project by New Year’s Eve. On regular visits to the line’s three new stations, he obsesses over design details and equipment glitches at a surprising level of involvement for a governor, which some critics say seems primarily aimed at promoting his image.