Adjustable voltage regulators

The "IGN" terminal of a regulator is voltage setpoint. A regulator switches field on and off as necessary, to control average field current, resulting in voltage regulator. More field current, results in higher output voltage. Switching happens quickly, such that when reading with a meter, average voltage is present. Field inductance and battery filters to a fairly smooth voltage. Electronic regulators are much less noisy than mechanical.

A regulator is much like a thermostat for a heating system, you set thermostat for desired temperature. If room is cooler than setting, heater is switched "ON", if at or
above desired temperature, heater switched "OFF".

Feeding a battery is a bit more complicated, it is a chemical thing. Chemical activity increases with temperature. Regulators are designed to slightly increase setpoint voltage when cold, and decrease when hot. High end charging systems actually monitor battery temperature, but not found on early mopars. They assume under hood temperatures, same for regulator and battery.:).

Measuring "IGN" voltage, at 75F might read about 13.8V, with running engine, and be higher, 14.2V if cold. Reading battery will be slightly higher, due to voltage drops. Del has good post #4.