There are two types of grounding wires: home ac or AC, and car DC or DC. The domestic ground wire should not carry any current at all during normal operation. Although commonly referred to as a 12-volt circuit, a DC ground wire in an automobile type circuit will actually carry 12.6 volts of electricity to complete the circuitry in the automobile type wiring system. The system can be in a car, motorcycle or truck.

Step 1

Set your megometer to read 120 v AC to test the home ground wire. You will use it as an ammeter to measure the voltage between two points.

Step 2

Flip the circuit breaker to the "off" position on the ground wire circuit to be tested.

Step 3

Use a screwdriver to unscrew the ground wire from the electrical ground column. Pull the wires from the terminal and keep the ends accessible.

Step 4

Flip the circuit breaker for a particular circuit to the "on" position.

Step 5

Contact the ground wire with a probe from the megohm meter, and then contact the ground wire electrical terminal with a probe. Because your megometer is now acting as an ammeter, it will record any current flowing between the post and the wire. A properly grounded wire will display zero voltage.

Step 6

To test a DC grounding wire, pull it from the device it is connected to, such as a radio, heater fan, or cigarette lighter. Set your megometer to 20 VDC. Contact the end of the ground wire with one probe and the electrical terminal of the equipment with the other probe. Check the voltage reading. It should be zero. In addition, it means a broken wire reading of 12.6 volts or a short circuit of the ground wire reading of 12.6 to 0.