The Post is having everyone but David Berkowitz wax rhapsodic about the summer of 1977 — wait, maybe that's the big final installment! — and today it's Mayor Koch's turn to brag how he "Helped Put Juice Back in the Big Apple" (despite the fact that he wasn't the mayor yet when the blackout hit — merely a candidate). So, where was Candidate Koch when the lights went out? The perfect place, it appears. "On the 17th floor of an apartment house being interviewed by a citywide gay caucus," he writes. "I told them that within the first 30 days of my administration, I would issue an executive order prohibiting discrimination by government in employment or housing based on sexual orientation." Um, Ed? The task was to reminisce about the blackout, not to suck up to the people who still detest your inaction on AIDS. But go on! "The room … suddenly went black and the meeting ended. I walked down the 17 floors to my campaign bus." Leaving the gay caucus, as it were, in the dark.