Voltage Drop
Checkingvoltage dropin your car electrical connections can help you locate current resistance that might be preventing one or more electrical components from working. This simple test can reveal loose or broken wires, corroded or rusted connectors that could be affecting your battery, electrical window, light bulbs and many other electrical units. Without a proper test, you can spend a lot of money and time replacing components unnecessarily. However, to perform a voltage drop test, all you need is avoltmeterand a few minutes to troubleshoot suspected wires or connectors.Preparing for the testOn your voltmeter, select a range just above battery voltage. Selecting 15 or 20 volts on the Direct Voltage (DV) scale will work just fine. For this test, you'll need electrical current going through the circuit you are testing. Block the wheels of your car with a piece of wooden block, start the engine and apply the parking brake. Let the engine idle.Make sure to keep your hands and wires away of moving components during this test. Now, connect your voltmeter's red lead to the metal connector or wire on the side of the connector, switch or terminal you are checking that is receiving positive battery voltage, and connect the other lead to the metal connector or wire ground of the same component your are testing.If you are testing the positive battery terminal for voltage drop, for example, touch the positive battery post with the red lead of your meter and the battery terminal that connects to the terminal of the same battery post with the black lead of your meter. If you are testing the other battery terminal, you would reverse the leads. Many digital voltmeter are equipped with polarity auto-correction, which let's you hook up the leads in reverse order. However, you'll see a minus sign next to your voltage reading, indicating you have connected the leads backwards.Performing the voltage drop testAfter you've hooked up your voltmeter's leads to the terminal, connector or switch you are testing, turn on your voltmeter and read the voltage on the meter's display. A voltage drop greater than 0.1 volts, usually indicates current resistance. If you are testing a battery terminal, for example, corrosion could be preventing full battery voltage from going through the terminal. If you are testing a sensor or actuator connector, rust orcorrosioninside the connector may be blocking electrical current. Or, if you are testing a switch, the contact points may be burned or pitted. Examine the terminal, connector or switch and remove corrosion or rust, if necessary.If the voltage drop is too high, current might not be going through that part of the circuit. In this case, check for a disconnected or loose wire on the terminal, connector or switch. As you perform this test, move or wiggle the wire on the connector or terminal and see if your voltage drop changes. If it does, you might be dealing with a loose wire.A voltage drop test can reveal voltage loss or electrical resistance that might be preventing electrical components on your car from working as they should. Loose or broken wires, corroded or rusted terminals are hard to detect without a proper test. You can perform this test as part of your troubleshooting procedures when you suspect electrical problems on any of your vehicle's electrical circuits. This simple test can help you save time, money and headaches.
