I have more than 40 years experience measuring DC currents in mining including locomotive applications of more than 1000 amps. I have sized external shunts for the older style 0-1 milliamp meters so that the Full scale milliamp corresponds to whatever max amp the circuit needs, and also used various Hall Effect clamp on meters. I own Fluke direct measuring multimeters that go to 20 amps, and have the Fluke clamp on Hall Effect attachment that measures up to 400 amps at 1 millivolt per amp.
If someone will give me part number(s) for Chrysler meters that are typical for older cars and pickups i would be willing to stop by a local to me parts store with my meters and measure the shunt and how many milliamps it takes to move the meter full scale.
I would guess the shunt for an automotive gauge of either 0-60 or 0-80 full scale amps is a thin but noticeably wide bare metal bussbar set on spacers to allow heat dissapation.
https://www.amazon.com/DROK-Anti-Rust-El...nt+less+ammeterI would be surprised if the guts of the meter movement is not the almost standard 0-1 milliamp.
When new and clean of corrosion at the screw connections I would guess that the shunt buss-bar surface temperature is less than 40 degrees F more than the air cooling it. Safety concerns would lead me to believe that Chrysler would desire a max shunt temperature of less than the flash point of gasoline vapor on a 115 degree Death Valley day during severe duty vehicle testing.
It is possible that Chrysler used a precise length of 6 gauge or heavier wire to provide the shunt resistance, as the ohms is usually way less than 1 ohm, and 0.01 ohms is not unusual.
Wouldn't the FSMs of those years have an ammeter test proceedure,
something like:
turn on the headlights when the engine is off and battery at 12.6 volts
and check that the ammeter reads 20 amps of draw?
