Diagnosing an inoperative circuit comes down to answering these three questions. This lessons identifies and explains these three questions.

If the Battery voltage changes when the car is running, how will this affect the voltage reading we expect at different parts of the circuit?

Let's take a look.

What happens if the Resistor Values are Different. Yes, you guessed it... the Voltage Readings for each Resistor will be different.

This video demonstrates voltage measuring expectations and actual measurements using two 50 Ohm Resistors connected in Series.

This video discusses the reasoning behind why you might choose a "voltage drop" ' measurement vs a "voltage At" measurement. Sometimes there is a choice, and sometimes it is just best to use the one best choice for the situation. Let's investigate.

This video continues the discussion on the reasoning behind why you might choose a "voltage drop" ' measurement vs a "voltage At" measurement.

High resistance or unwanted resistance causes an undesirable voltage drop in the circuit. This unwanted voltage drop robs some of the necessary voltage needed for a circuit to operate properly. High resistance can be present in the power part of the circuit or the ground part of the circuit. This lesson demonstrates these conditions.

Power or Ground side voltage drop caused by high resistance across switch contacts, wiring connectors, and components steals some of the voltage available causing the circuit to not work properly or to not work at all.

This lesson describes the basic components and wiring layout of the brake and park lamp circuit. This system schematic will be used in upcoming case studies.

This first case study provides diagnostic practice using the schematic to narrow down the possible faults. Our job is to act like a detective and eliminate what we know has to be good and then make a minimum number of tests to pinpoint the exact problem.

This lesson provides a description and operation of the horn circuit that we will be using for our next case study.

In this horn circuit case study, pay attention to the diagnostic thought process and the way the fault possibilities get narrowed down. Think about how much time can be saved by understanding the circuit and having to possibly make only one or two test on the car.

Remember that when there is a fault in an electrical circuit, one of the big three power, load, or ground is missing or defective. Let's review power, load and ground before we get into some more advanced special situations that can occur when dealing with high resistance problems.

This lesson describes a special situation that can happen that looks light it may be high resistance, but is in reality, is an open in the ground path. Let's look into this tricky scenario so that you won't be fooled when it happens.

This important video demonstrates high resistance in the power path and in the ground path. It walks you through the thought process and explains what to do when you do not get the readings you expect when making tests.

In this demonstration lesson, we will show why a "voltage drop" measurement is not a good choice when dealing with a circuit that is not working at all. "Voltage At" measurements are the best way to go in these situations. In the real world, you do not have to go through the circuit one connection at a time and test at every location. You would pick the easiest to access spot that makes sense based on the schematic and component locations. Then, the reading that you get would tell you which direction to go.

This lesson covers a less obvious high resistance issue that can lead to false diagnosis of module power and ground circuits. High resistance is only visible on the meter if the circuit is on. If you create an open by disconnecting a part of the circuit to make a test, and then you leave that part disconnected, you may get confused by the result. The high resistance is not visible to your tests until you reconnect the wiring you disconnected and power up the component.

Let's look at the benefits of some additional diagnostic tools for testing electrical circuit faults. It is important to remember that these specialty tools are not a substitute for knowledge. They may help short cut the time it takes for testing, but if you have the wrong thought process, you will not come up with a correct solution.

This lesson discusses some of the safety practices you should understand and implement in your diagnosis and repair of vehicles.

This lesson discusses some of the quick checks you can make when your are maintaining the vehicles you work on.

This lesson discusses how to configure and maintain robust electrical systems. Always check and test the battery when possible, especially if there is an electrical problem. So many error messages and warning lights can be triggered by low voltage conditions. Also check for any service bulletins that may apply to a specific issue you are trying to diagnose. Dealer employees have access to these updates. Do-it-yourselfers will have to try online searches and forums. It is best to search by VIN when possible and not just by year, make and model.

This lesson discusses and provides a downloadable checklist that can be used to help you monitor the health of a vehicle's electrical system.

Thank you for taking this course. I hope it has provided you with a better understanding of high resistance and voltage drop diagnosis and testing.

Best regards,

Steve Liguori

autoelectricaledu@gmail.com

This last video demonstrates a real world scenario that can drive a technician crazy. Take a look and see if this type of issue has ever happened to you.

Thanks again for taking this course.

Steve