noob questions about oil pressure and brakes.. please help!!

so i bought a 97 cadillac deville, with 110k on the northstar, for my father a couple of days ago, and everything was fine up until the time i was almost home.. the oil light kept flickering at idle and at one point it started telling me to stop the engine cause it had low oil pressure.. i pulled over and checked the dipstick and there was plenty of oil in there..
i did a search on here and came up with the conclusion that it might be the oil pressure switch, and i know its somewhere near the oil filter but i dont know where exactly this is.. i was wondering if someone could tell me in detail or post a pic of where it exactly is and how i go about replacing this item..
one more thing, the brakes were vibrating every time i would try to stop.. i concluded that the rotors must be warped, so i replaced them and new pads in the front, but it still does it.. i asked a friend and he told me the caliper bolts had to be torqued down to a certain amount.. if someone could tell me if this is what has to be done and if so what the exact amount is i would really appreciate it.. thank you all in advance..
-TUNA