Low Charging Voltage

If you remove the green wire on the alternator and short that alternator terminal to ground the voltage across the battery should go to 15+ volts and higher as the rpm increases. If that happens then you have a good alternator. If it doesn't then make the same measurement to ground from the output terminal of the alternator if you get the 15+ there then you have bad connections between the alternator and the battery. If you don't then the alternator is bad.

The blue wire on the alternator when removed from the field terminal and the key in the run position should measure within 1/2 a volt of what the battery voltage reads. If it doesn't you have bad connections some where. The green wire on the alternator makes a connection to ground through the regulator body. With the key in the run position and the engine not running the resistance from the terminal on the wire at the alternator to ground should be within an ohm of zero. If its not you have a bad ground connection at the regulator or a bad regulator.

I would make sure all your ground connections are good. If you don't have them I would add a ground strap or two between the block and the body. I would also use toothed star washers under the fasteners holding the regulator and ground cables.