What Chrysler made after 1975 is replace the full load ammeter for a shunted ammeter system which it works like somehow of remote ammeter. The ammeter got an amplifier coil to increase magnetic field able to move the needle with a minimal load going parallel to a shunt wire ( on engine bay ) offering a slight resistance to the charging system which allowed to get some minimal load going through the shunted ammeter. But not a resistor on ammeter really.
Ammeter NEVER READS VOLTAGE... just magnetic fields variation caused by electrons which feed the load requirements
https://en.wikipedia.org/wiki/Shunt_(electrical)#Use_in_current_measuring
"An ammeter shunt allows the measurement of current values too large to be directly measured by a particular ammeter. In this case, a separate shunt, a resistor of very low but accurately known resistance, is placed in parallel with a voltmeter, so that all of the current to be measured will flow through the shunt. The resistance is chosen so that the resultant voltage drop is measurable, but low enough not to disrupt the circuit. The voltage across the shunt is proportional to the current flowing through it, and so the measured voltage can be scaled to directly display the current value."
https://en.wikipedia.org/wiki/Current_sensing#Shunt_resistors"Ohm's Law is the observation that the voltage drop across a resistor is proportional to the current going through it.
This relationship can be used to sense currents. Sensors based on this simple relationship are well known for their lower costs, and reliability due to this simple principle. "
