The voltage and current regulators are in series with each other. They perform an either/or function. When charge current is high, the current regulator prevents overloading the armature when charging a very low battery. Once the internal resistance in the battery rises the voltage is controlled by the vibrating points behind the field terminal. If you have an oscilloscope, you can monitor a modified square wave at the field terminal by the open/closed action of the points- - - -several times a second. Try burnishing the CR and VR points with VERY fine wet/dry sandpaper (1500 grit) and alcohol, followed by a thorough scrubbing with a piece of a clean index card or a business card. The contacts are pure silver, and are VERY soft. DO NOT USE A FILE! They operate with a slight wiping action for self-cleaning, and file scratches will make them stick. With both points closed, the resistance between the F terminal and the regulator base should be almost zero.
You can simulate a fully charged battery by putting a 1/4 ohm resistor in series with the BAT terminal. I use four 1 ohm 1K watt ceramic resistors wired in parallel for that. Final voltage adjustment MUST be done against a fully charged battery to get a proper setting. Both current and voltage settings will drop slightly when the steel cover is installed- - - -better magnetic conduction. I've been doing this stuff for 65 years. "It's so simple even an electric train driver can do it!"
Jerry
