Have you tested the battery? A faulty battery may not take a charge and will confuse the VR which monitors battery voltage. Have the battery properly tested after it is at least 50%charged with a disconnected standing charge of 12.2V or higher. Confirm your battery connections are clean and secure. Confirm the VR and alternator is grounded with clean, secure fasteners. Bypass the dash-mounted ammeter by running a heavy jumper wire from the alternator positive post to the battery positive post and then check high idle voltage, 13.2V-14.8V give or take a 1/10th. Confirm continuity on the green field wire between the VR and the alternator with an ohm-meter while both ends are unplugged. Should be less than .5 ohms. Wiggle the wire harness while testing to check for concealed breaks in the wire.

FYI: Your VR supplies a ground for the alternator field. It's a cycling switch. When the green field wire is grounded through the VR the alternator's magnetic field grows and produces an increase in voltage output. It connects and disconnects the ground rapidly to regulate the strength of the field. The VR monitors battery voltage that's coming through the ignition switch to determine the duty cycle of the grounding of the alternator field. When you full-field the alternator your duty-cycle is 100% and the alternator produces maximum output in voltage and heat.

The power for the field also comes through the ignition switch.

The alternator output goes to the ammeter in the cluster to swing the needle and then goes to the battery usually by way of the post on the starter relay. From there the current is distributed to the battery, starter solenoid, and fuse box for further distribution. You can check this wire by either by bypassing it or performing a voltage drop test.

You can perform a voltage drop test on any positive or negative circuit when current is flowing, or supposed to be flowing. With the engine at high idle, turn headlights on to load the alternator. Connect a digital voltmeter (don't use one with a swinging needle, analog) between the battery positive post and the alternator output post. DVOM common lead (black) on the battery positive and red lead on the alternator positive post (positive to positive). The voltage drop should read no greater than .5V. (half a volt). You can do the same with the ground. Alternator case to battery negative post (ground to ground), again expect a low number of .1V to .3V. High numbers, above .5V, mean there is an open or high resistance in the circuit. Older cars may see as high as .8V and be OK.

Let us know what you find.