Theory Of Operation

Voltage drop is the reduction in voltage in an electrical circuit between the voltage source and load components. The wires and connectors of a circuit should contain almost no resistance and all  the voltage should be consumed through the load. The "load" is the component using the power, such as a light, starter, or blower motor. If a circuit has excessive resistance, it prevents the wire from carrying sufficient current under high load conditions. A voltage drop test is an effective way to locate excessive resistance in connections and circuits.

To perform a voltage drop test, a Digital Volt Ohm Meter (DVOM) is used to measure the voltage drop across a live circuit or connection while it is under the load. If the circuit or connection being tested has excessive resistance, the DVOM will measure the voltage that the resistance is using. Little or no voltage drop should be read, ideally less than 0.2 of a volt  , anything greater indicates excessive resistance and the circuit or connection should be inspected for cleaning or repair.