The one plaguing my Late 2006 MacBook is the tip contact. Staring into the glowing red Cylon eye, they are: 2 'sleeve' contacts (nearest you), one at 9 o'clock and one at 3 o'clock (positions on an imaginary 12-hour analog clock dial) 1 'ring' contact (farther in) at 12 o'clock and 1 'tip' contact (all the way in) also at 3 o'clock. The Apple 3.5mm headphone jack may have multiple different failure modes, since it contains 4 equally flimsy electrical contacts.
