My friend, who doesn't really play guitar much, let me borrow his 1993 MIM strat that his uncle gave him. I've been trying to fix it up, and what has stumped me is the middle pickup. It just doesn't work. In positions 2, 3, and 4, the middle pickup produces no sound. I unscrewed the pick guard and looked for loose connections and things like that, but everything seems in place. There is buzzing, as if something isn't grounded correctly, but I can't see where. Is there something I should check? Something simple I'm missing? I'm not very familiar with strats, so I don't know what to really look for.