[rotorwrench]

Most ammeters for automotive use have no markings on the terminals. The reasoning is simple. They are made so they will work with either polarity, ie negative ground or positive ground. One side connects to the generator or alternator and the other side connects to the load which is also interconnected to the battery. On more complex systems with higher voltages and amperage capability a shunt or shunt wire is generally used so that it won't overpower the ammeter. The shunt allows the ammeter to read a sample of what current is passing through the cable between the generator or alternator and the electrical buss that all other systems tap their power from which includes the battery storage.

If a freshly installed ammeter reads discharge with a system that is known to be functioning correctly, the leads will need to be swapped on the ammeter terminals so it will read correctly. Ammeters are always connected in series. If a person connects a terminal to ground then it will make a load out of the ammeter and fry it or the wiring.