In this video, voltage drop testing is used to measure the voltage loss between two points in an electrical circuit. This testing is used to diagnose problems in a vehicle's electrical system, such as issues with the battery, alternator, starter, or wiring. A multimeter is used to measure the voltage at two different points in the circuit. The first measurement is taken at the power source, such as the battery, and the second is taken at the point where the problem is suspected. The difference between these two measurements is the voltage drop. We use two snap-on meters in the video to perform the voltage drop testing. The first meter measures the static voltage at the battery, while the second meter measures the voltage drop at the fuel pump fuse. By comparing these two measurements, we can determine if there is a significant voltage drop in the circuit and identify the location of the problem. It's important to note that voltage drop testing should only be done by a qualified technician, as it involves working with live electrical circuits that can be dangerous if mishandled. Additionally, to perform voltage drop testing correctly, the circuit should be loaded, and the vehicle should be running. In general, the ideal voltage drop across a circuit should be as close to zero as possible. A drop of more than 200 millivolts is considered excessive and may indicate a problem in the circuit.