Chapter 9 Basic Electrical Tests 187 Copyright by Goodheart-Willcox Co., Inc. Summary • Most circuit problems are caused by something very simple, such as a broken wire or loose terminal connec- tion. However, when this basic trouble is in a complex circuit, it can be very diffi cult to locate and repair. Correct techniques must be used to fi nd electrical prob- lems in a modern vehicle. • Use a systematic approach to diagnose electrical trou- ble. First verify a problem and analyze the symptoms. Th en narrow down the possible causes for the problem. Perform the proper tests to fi nd the exact trouble. Aft er making the repair, recheck to be sure the problem has been corrected before releasing the vehicle to the customer. • If only one component does not work, start your tests at that component. If several components in the same circuit are not working, start your tests at the power source to the circuit. • Common circuit problems include an open circuit, high circuit resistance, short circuit, and intermittent circuit problems. • Jumper wires, test lights, inductive circuit tracers, and multimeters are important testing devices and can be used to fi nd most types of circuit trouble. • A voltmeter must be connected in parallel with the circuit. A conventional ammeter must be connected in series with the circuit. An inductive ammeter has a lead that clips over the outside of the wire. An ohm- meter must not be connected to a source of power. It uses internal batteries to measure circuit or component resistance. • Voltage drop measurements provide an easy way of checking for high resistance. You do not have to discon- nect the power source and isolate the component, as with an ohmmeter. A high voltage drop indicates a high resistance. A low voltage drop indicates a low resistance. • Learning how to perform basic tests on connectors, resistors, switches, fuses, and other basic components will help you understand how to test more complex components. Review Questions—Chapter 9 Answer the following questions using the information provided in this chapter. 1. What is the meaning of the saying “Veronica never touches much voltage”? 2. What are fi ve questions you might ask yourself when trying to fi nd a problem? 3. If only one component does not work, where should you start your tests? 4. If more than one component does not work, where should you start your tests? 5. What eff ect does an open circuit have on current? 6. What six conditions may cause an open circuit? 7. What might make a bulb glow dimly or a motor run slowly? 8. Explain how a short might cause an electrical fi re. 9. What is an intermittent problem? 10. How would you use a jumper wire to check a switch? 11. Which testing device usually provides the quickest and easiest way to check a circuit for continuity? 12. Which testing device uses a signal generator and inductive pickup to fi nd shorts and opens in wires? 13. Explain how to connect a conventional ammeter and an inductive ammeter to test a circuit. 14. An ohmmeter shows a reading of 2.500 kΩ. What is the meter reading in ohms? 15. Explain how you can use voltage drop measurements to determine whether a switch is functioning correctly. 16. List eight rules for using multimeters. 17. Which type of multimeter should be used to check for voltage in a computer circuit? 18. Explain how to use a test light to check a connector. 19. What three testing devices might be used to test a switch? 20. What is the most accurate way to check a variable resistor?