Ammeter Resistance and Voltage drop

Stihl011 said
Both the always on and the accessory supply are attached to the alternator side of the ammeter. I am seeing a resistance between the positive battery cable and the alternator be about 5.3ohms,

Are there two wires attached to the alternator side of the ammeter?
On a standard wiring harness there should be one. A second wire there would be some sort of option.

There should be no measureable resistance between the battery cable positive erminal and the alternator's BAT terminal.

Stihl011 said
and a nominal voltage drop of about 1.5V-2V between the battery voltage and the alternator voltage when the car is off.

There should be no voltage drop when the car is off.
Something had to be running. Was the door open or your foot on the brakes or ?

Stihl011 said
I am also seeing what I believe is WAY too much resistance from the starter switch between the alternator side of the ammeter and the accessory output of that switch. I believe this to be my primary issue, because when in accessory or run, I can watch the resistance change between 5 and 50 ohms just by moving the key around. If this accessory output voltage is drooping more due to this high resistance, then maybe that voltage input turning is triggering the turn off. The only thing that makes me question this is I can watch both input voltages with the o-scope, and I don't see one significantly different than the other, the accessory is maybe 0.5V lower at all times,

Not sure how/where your measuring voltages but agree there should be only small resistance in the key switch. 5 to 50 ohms is huge.

Stihl011 said
In short, can anyone tell me what is anormal value for voltage drop between the battery and the alternator when the car is off, and/or what resistance I should be measuring between the battery and alternator? I may have both problems here.

The first can only be answered when the currrent is known.
If the ammeter shows 10 amps, then there may be a bit of voltage drop. If it shows 0 amps the voltage drop must be zero. V=IxR

I'd like to see zero resistance using standard meter.
Note that meters use small voltage difference to measure resistance. (most modern meters have a battery)
So can't measure resistance if there is currents flowing in the system

Stihl011 said
In summary, with car off
Battery Voltage: ~12.5V
Alternator Voltage ~10.5V
blinker or brake lights drop alternator voltage to ~8V temporarily.

System voltage should not drop to 8 volts unless the battery is badly discharged.

The main power circuits for a standard 1968 Barracuda

With the engine off, the ammeter will indicate current flowing to anything turned on. ie Battery Discharge
With the engine running, the ammeter will indicate current to recharge battery. ie. Battery Charge
But the ammeter will not show current flowing from the alternator to any other equipment.