Generator light on; only getting 13V.

[BB69]

I'm hoping you guys can help me out with this one. My generator light is on, and I can only get the alternator to put out about 13V. Here is a run down of how my system is setup:

battery in trunk
remote solenoid in trunk as well
8 gage wire from battery side of the solenoid to a junction on the firewall
10 gage wire from alt + to same junction
10 gage wire from voltage sensing terminal on external regulator to same junction
main power wire for dash connected to the same junction
brand new alt as of yesterday
brand new external voltage regulator as of yesterday
optima yellow top

I get the same voltage readings whether it's at the + terminal of the alt, at the battery in the trunk, or at my junction on the firewall, so I don't think it's a problem with grounds or voltage drop in any wires.

My car has been apart for over two years, and I just got it back together. I can't figure out what's wrong. The only part of the charging system that has not been replaced is the small cylinder that attaches to the voltage regulator.

Any help is appreciated. I looked through the archives, and could not find any threads where someone actually solved a similar problem.

Thanks
Ken