There’s a notorious scene in 1980 thriller Cruising that might be the best fictional time capsule we have of a wanton, unfettered gay dance floor just before AIDS hit. Director William Friedkin was still swimming in the success of The Exorcist when he decided to take on the prescient tale of a serial killer haunting New York’s BDSM community, leaving tortured and often unclaimed bodies in his wake. Al Pacino plays the cop who goes undercover to catch the masked murderer, discovering new dimensions of his sexuality along the way.

To catch a gay killer in those days, you had to start on the dance floor, the epicenter of the fellowship. As Pacino slips on a black tank top and studded cuffs and snakes into the Ramrod bar for reconnaissance, you feel Friedkin’s camera reveling in this secret world of burning stares, flashing chaps, gyrating trios, and loaded slings. Not all gay-centric discos were like this, of course: Liza Minelli would soon be doing the cha-cha under a giant coke spoon at Studio 54, and Paradise Garage focused more on musical innovation than masculine amalgamations. But thousands of Ramrod-like kink dens, backroom booths, adult bookstores, and bathhouses existed across the US — Cockpits, Anvils, Eagles, Badlands, Baracks, Rawhides, and Hungry Hole Saloons. This was certainly, however, the first time one appeared in the shopping mall multiplex.

In the dim light of the bar, the film’s colour palette drains to blue and black. Pacino is tempted to the dance floor by a fetching lad who promptly hands him a rag soaked in amyl nitrate, aka poppers, a sexual stimulant. As Pacino puts the rag to his face for a hearty sniff, the scene suddenly bursts into full colour, and an American flag on the wall strobes with electric lights. It’s a perfect analogue to the effects of the drug, and a nod at the country’s lightning-rod relationship to its homosexual citizens who, ten years after the Stonewall Riots launched the gay liberation movement, were basically sexual outlaws hiding in plain sight.

Suddenly, Pacino’s limbs are flailing and head shakes in a blur. He’s into it. Like, really into it. The only hitch is that the scene is soundtracked all wrong. Instead of a swelling, hypnotic climax, we get a cheesy, upbeat rock number called ‘Heat of the Moment’ by Willy de Ville (not, alas, a pseudonym invented especially for the movie). It’s not exactly terrible, but it’s definitely not what any self-respecting sex dungeon of the time would pump.

In fact, by 1980, there was a very specific type of music tailored to accompany such scenes of debauchery: one that grew from the protest and experimental music scenes of the ’60s, melded elements of psychedelic and prog-rock to disco; meant to enhance the excitement of man-on-man cruising, illicit sex, and chemical stimulants through electronic means.