From 2Pac's rap classic "How Do U Want It." In it, 'Pac says "I'm hittin' switches on bitches like I been fixed with hydraulics." The phrase means that you make all the nastiest, smoothest moves when it comes to sexin' your lady of choice. For added effect, many times one might pretend to be flipping switches and make a variety of sounds that might be heard on a car with hydraulics, because that "bitch" was bouncing up and down and putting on quite the show. Well done.
"When I was breaking in that one trick from the bar last night, I was hittin' them muhfuggin switches, boy!"