ampere guage

The only thing that I can figure is that they are using the wire between the alternator and the battery as the shunt. Connect one terminal to the positive post of the battery, and connect the other to the output terminal of the alternator. Have someone inside the vehicle to make sure the meter does not peg out. (I do not think it will) Start the vehicle, notice the reading, then turn your headlights on, notice if it moves the meter. If it moves the wrong way, reverse the battery and alternator connections.

I have no idea what kind of vehicle we are dealing with. If you upgraded the wire from the alternator to the battery then maybe yes. If no upgrades have been done, I really doubt that it will have a 4 Ga. wire. An 8 Ga. or maybe a 6 Ga., but doubtfully a 4 Ga. It will be the largest wire connected to the alternator, and the positive terminal of the battery.