Google " Chrysler master tech video" you can add a word to the end like "gauges"
And you will get a result of videos like this one:
They are corney BUT very helpful.
I don't know your knowledge of old cars so bear with me.
The alternators on our cars work great at engine RPM over about 1500.
They don't work so good at idle especially at night with headlights and brake lights on.
This is normal and nothing to worry about, ASSUMING all the rest of the electrical system is in good shape.
Some things that can cause flickering in your lights:
is a bad diode in the alternator. The alternator produces AC and the diodes convert the AC to DC. If a diode fails it can allow some AC onto the DC wires. This can cause a flicker. The parts store tester should be able to see that.
The stock voltage regulator is an electro mechanical device. It has contacts and depending on the load requested by the car will open and close faster or slower. If the regulator is having issues it can produce a voltage fluctuation that would look like a flicker.
Grounds as stated before
The 3 bulkhead connectors as noted before are a weak spot on our cars. They get corroded and build resistance that makes heat and the heat melts the plastic and weakens the metal terminals.
The headlight switch is another location like the bulkhead connectors check & clean
The ammeter is a passthrough device. When in good shape it works great, but it can get internally damaged and the connections get weak and build resistance & heat etc.
Some remanufactured alternators use a 3" dia pulley when the factory calls for a 2.5 to 2.75. this slows down the alternator and exaggerates the low RPM performance.