An ammeter is often called an amp meter. It is a device to measure electrical current in units called amperes. Ammeters were used in vehicles such as automobiles and motorcycles, and they were used in these situations as an indication of whether or not the battery was being properly charged. They not only show the amount of current flow, they indicate the direction of the current flow. They can do this because batteries supply a direct current (DC) voltage. When the vehicle engine is started, current flows out of the battery. When the engine is running, current flows back into the battery to recharge it.
Locate the vehicle's battery and positive terminal. The positive terminal will sometimes have a plus sign (+) near it and have red cables or wires connected to it. Wear safety goggles and work gloves when working near a vehicle battery.
Disconnect the red wire from the battery that goes to the alternator charging terminal. Disconnect it at both the alternator end and the battery end by using a socket wrench. You can use wire strippers if the terminals cannot be loosened.
Connect a 14 gauge wire from the battery's positive terminal to one terminal on the ammeter. Tighten the hex nut over the eyelet terminal on the wire at the ammeter.
Tighten one end of a second 14 gauge wire to the other terminal on the ammeter. Route the wire to the charging terminal on the alternator and tighten the nut there.
Go back the battery's positive terminal and tighten the connections.
Allow the vehicle engine to cool off before you begin working on wiring an ammeter.
Batteries can create toxic chemicals. Use caution when working with vehicle batteries and wash your hands after working with them.