Here's an odd question: Are you sure the meter is OK? If you connect it to the battery, with the car off, are you seeing "12" volts?
if the meter is good (on the right scale, etc.) and the alternator bench tests as good, then the alternator 'excitor' isn't exciting the alternator. That is, the alternator is not getting
power (from your battery via the ignition key) to excite itself, and without that little tickle it can't put out
power from the main output.
Your picture looks like a typical Delco...in which case, #4 is a test point, and #2 and #3 are the critical wires going out to your harness and key. Those circuits need to be completed properly, or you'll get no output, regardless of how fast the alternator is spun.