Voltage-drop testing is one of the most useful and effective electrical checks a technician can perform. Owners and managers should understand this technique and encourage it. My field experience has been that many bosses don't have a clue as to what voltage-drop testing is or why it's so valuable. Therefore, they don't promote the technique nor do they charge accordingly for it. I'm often told that the topic is far too complex for a non-technician to understand. I disagree with that attitude. I've always found that electricity is only as complicated as people want to make it. In that spirit, let me present a brief primer on voltage drop testing. I'll bet you a tire plug that this isn't as difficult as you thought. First, electrical volume is called current, which is measured in amperes. The key thing to remember is that current must flow freely from the battery out to the vehicle's electrical devices. Then the current must flow freely through each device and back to the battery again. Statistically, circuit restrictions are the No. 1 cause of electrical breakdowns and electrical symptoms. The common causes of restrictions are loose, broken or corroded electrical connections and/or frayed or broken wires. When these conditions restrict the free flow of current, an electrical device works intermittently, works incorrectly or stops working altogether. Now suppose we're discussing a restriction in a headlight circuit. Depending upon the severity of the restriction, the symptom could be a dim headlight or one that lights up intermittently. Or maybe the headlight doesn't light up at all. So, to recap briefly, the job a motorist is most likely paying you to do is to pinpoint and fix a restriction somewhere in an electrical circuit. Interestingly enough, measuring current isn't the way to pinpoint an electrical restriction. Rather, the way to pinpoint the restriction is to measure electrical pressure. Electrical pressure is commonly called voltage—measured in volts with a voltmeter. Let me continue with that simple example of the headlight. The current should flow freely from the battery to the headlight. That's called the supply side or positive side of the circuit. Then the current should flow freely through the headlight and back to the battery. The return path back to the battery is commonly called the negative side or ground side of the circuit. In a healthy circuit, voltage (pressure) drops a little bit as the electricity flows from the battery out to the headlight. The voltage also drops a little bit as the electricity flows from the headlight back to the battery. But if there's a restriction between the battery and the headlight, the voltage will change substantially. A tech can measure this change with a common voltmeter. What's more, the tech can follow the circuit, observing voltage along the way. A sudden, severe change in voltage always occurs at the exact location of the restriction. Obviously, finding the restriction quickly and accurately is the key to profitable electrical repair. At the very least, the voltage measurements tell the technician what section or “leg” of the circuit contains the restriction. That way, you're better prepared to estimate how much time it will take to access that part of the circuit. This knowledge enables you to communicate the details to the car owner—and sell the repair—more accurately and confidently than your competitors can. To me, a very basic understanding of voltage testing—including the voltage drop technique—should enhance sales of electrical repairs. It also should help service sales professionals control the transaction more effectively by selling the diagnostic and repair time necessary to do the job. There's no circumventing that time investment if you want to fix the vehicle correctly the first time.
Selling electrical testing's not difficult
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