An ammeter is used to measure the amount of current flowing though a wire in a circuit. The size of the ammeter will vary by the amount of current that needs to be measured. For small circuits under 10 amps and 12 volts or less, the ammeter is usually connected in the circuit to allow all of the current to flow through the meter. Automotive battery testers can also be connected within the circuit. Larger current circuits with deadly voltages use inductive ammeters. These meters use the magnetic field produced by the current to calculate the current.
Connect the positive alligator clip of the test light onto the positive terminal of the battery. Connect the negative terminal of the test light to the positive probe of the ammeter or multimeter. Make sure the multimeter is set to the 10 amp setting. This method is for small 12 volt circuits under 10 amps.
Connect the negative terminal of the ammeter to the negative terminal of the battery.
Turn the ammeter on and check the readings.
Use a car battery tester at a mechanic's shop to test a car battery. These testers are designed to handle the high current produced by these batteries.