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Introduction
Some of the most difficult and challenging problems to solve are in the electrical system. Since electricity is invisible to us, we are reduced to using tools and devices to measure and verify it's presence. For this discussion we really need to understand a few things.
To test the starter circuit: Measure from battery positive post to cable end, then test each cable until you get to the starter. Then do the same on the negative side, starting at the battery post, and following it to body ground and engine ground. Then do it between body and engine. Remember, the circuit has to be under a load for this test to reveal the problem. Any voltage being displayed during the test reveals a potential resistance to electron flow.
A resistance test using an ohm meter is not an accurate way of determining if a battery cable is good. According to this ohms test, this battery cable is good!
A Voltage Drop Test can find all sorts of losses when used correctly on high amperage circuits. The circuit needs to under a load to perform the test.
Some of the most difficult and challenging problems to solve are in the electrical system. Since electricity is invisible to us, we are reduced to using tools and devices to measure and verify it's presence. For this discussion we really need to understand a few things.
- In order for electricity to flow, it needs to travel in a closed loop. If the loop (circuit) is not complete, we have only a potential circuit. So if we have no loop, we have no circuit, and no flow.
- Every circuit contains electrons. Even open circuits. Even a scrap of old wire is full of electrons. If you push more electrons in at one end, then electrons would flow out the other. Sort of like a conveyor belt. The more you put in, the more you get out.
- Any resistance in a circuit will reduce the number of electrons that are able to flow through it. Resistance can be poor connections, small wire size, poor quality wire, corrosion,
- Using the Voltage Drop Testing method on portions of the circuit while it under load will reveal the "restrictions to electron flow", by showing us a voltage differential on our volt meter.
- A reading of 0 volts when using this method is good. The higher the number, the bigger the problem.
- Voltage Drop testing can find problems on both the positive and negative side of the circuit.
- Voltage Drop Testing is ideal for testing higher amperage circuits, like starters, and alternators.
To test the starter circuit: Measure from battery positive post to cable end, then test each cable until you get to the starter. Then do the same on the negative side, starting at the battery post, and following it to body ground and engine ground. Then do it between body and engine. Remember, the circuit has to be under a load for this test to reveal the problem. Any voltage being displayed during the test reveals a potential resistance to electron flow.
A resistance test using an ohm meter is not an accurate way of determining if a battery cable is good. According to this ohms test, this battery cable is good!

A Voltage Drop Test can find all sorts of losses when used correctly on high amperage circuits. The circuit needs to under a load to perform the test.
