On my 1974 Dodge Ramcharger 4x4 truck, and others, the 30+ amps did run through the dash board. It was 10 awg wire, and connected to the ammeter with ring terminals over studs. If it used a shunt, it was built into the gauge. The current went through the firewall, and back, and that is where the fire occurred. Chrysler had some quality problems with their wires and connectors, and armed with the wiring diagram, I replaced a lot of wiring. I learned a lot about how they were wired. In all fairness, I did replace the original 37 amp alternator with a 90 amp alternator, and rev the engine to assist the winch which was rated to draw almost 600 amps. The heavy electrical load, caused the voltage regulator to make the alternator go to full output, and I quickly learned something Chrysler seems to also have learned. I haven't seem a similar design in years.
I wired my alternator output direct to the battery, and put a voltmeter in the dash. If the voltmeter reads above battery volts, the system is charging; if volts are low, the system is not charging.
Rod