If I were you, I would check the resistance with a multimeter and use the one with the greatest resistance in the neck, since they are of unknown origin. However, on the "no name" strat pickup sets (as well as "brand name"), the one with the red wire is the bridge, generally, and the white is generally the neck. But, to reiterate, if it were me, I would check it with a multimeter. You can get one at Wal-Mart or RadioShack for under 20 bones.
Sure enough, red wired pickup was highest resistance so I placed it in the bridge. Followed by yellow and then white at the neck.
Question: how come the poles in these pickups are all noticeably at different heights? I presume that this is done to alter the tone characteristics of the guitar (some string will sustain more or less or have more volume, etc).