1993 chevy k1500 truck charging system problem

I just finished an engine swap and lift kit install on my 1993 chevy k1500 truck (now has an engine, tranny, computer and wiring harness out of my 1989 k1500.) I went to drive my truck to the alignment shop and made it about half way there when the truck died. I should have done a few more tests before I left to prevent this, but here's the problem. I'm getting no charging from the alternator. I put a multi-meter on the battery terminals and without the engine running it showed 11.9V. With the engine running it also showed 11.9V. So, I took my alternator into the shop and they tested it and it seemed fine. I bought a new alternator anyway and installed it. Same problem. I also tested the voltage at the positive terminal on the alternator and it showed 11.9 when cold and when running. The only wires coming off the alternator are the positive terminal wire and a single wire plug that plugs in on the upper right side, I assume for the internal voltage regulator. So, I'm kind of stuck. Could be something really stupid. Any ideas? Thanks guys- I am guessing you are useing the older style alternator to match the wiring harness? If so there should be a 10 gauge wire power supply going to the stud on the back of the alt case. Connect another 10 gauge wire from the terminal #2 where it plugs into the side directly to this stud also.
The smaller 14 gauge wire #1 terminal is hot only when the key is in the on position and can be hooked directly to the battery for testing purposes but has to be to the switch to work correctly.
Make sure both red 10 gauge wires are hot constantly and the 14 gauge wire is hot with the key on and the engine running then it will work