Handbook 652 Body Electrical Diagnosis Voltage Measurements Two types of voltage measurement are: • Available voltage is the amount of electrical pressure (voltage) present at a test point in the circuit. • Voltage drop is the decrease in electrical pressure (voltage) between two points in a circuit. This is the amount of voltage used up between the two test points. In both of these tests, the circuit must be operating and current flowing. Both available voltage and voltage drop testing have their place in the diagnostic process. Information from each of these tests will be used to diagnose the most likely place to look for a problem in a malfunctioning electrical circuit.
Available Voltage When current is flowing and the negative probe is on a ground point, the voltmeter measures available voltage . In the example above, 12.5 volts is available to the lamp because a small amount of battery voltage was used up in the wiring before the test point. Only 0.05 volt is left in the circuit after the lamp, because most of the voltage was used up in illuminating the lamp. 18 Technical Training