Two of those posts are probably attaching screws that hold it to the dash. There should be only two insulated posts with wires attached to them. The one toward the passenger's side of the vehicle is most likely the one that should have only one heavy wire (10 gauge or larger)- - - -which goes to the battery cable terminal at the starter. ALL other wires should attach to the other terminal. Those will be the voltage source for the ignition switch, the headlight switch, the fuse block, and the wire going to the BAT terminal of the voltage regulator. Some ammeters have a long stud on one side that serves as a common junction block for all those wires.
If the system is wired correctly, ALL the current coming from the battery to the vehicle electrical system has to pass through the ammeter. the charging current also passes through the ammeter, once all the current demands of the ignition, lights, and accessories are met.
Jerry
