Electrical problems can comprise some of the most baffling automotive maladies, and can frequently be difficult to diagnose since there are often numerous components that might be the source of problem. For this reason, and because of some vital safety considerations, a few diagnostic tools are essential if you plan to work on your vehicle's electrical system.
A test light, sometimes called a line tester or circuit tester, is used to determine whether electrical power is being supplied to a given circuit, and/or whether the circuit is grounded. This is one of the most basic diagnostic tools, and one of the simplest to use. The one shown in our demonstration is designed for automotive use and features an alligator clamp on one end (figure A) and a probe on the other (figure B). To check for current, the clamp end is hooked to a ground and the probe is used to check the electrical circuit. Live current will cause the indicator light to glow. The reverse can be done to find a proper ground: simply hook the clamp end to a positive power supply and use the probe to test and identify a proper ground. In our demonstration, we identified which one of several wires supplies power to the driver-side turn signal. With the turn signal engaged and working, and the clamp end of the test light grounded, use the sharp end of the probe to gently pierce the plastic casing on each wire (figure C). When the probe comes into contact with the bare copper of the proper wire, the test light in the handle of the probe will illuminate. In the case where a particular electrical accessory is malfunctioning, and you know which wire supplies power to that particular accessory, the test light can be used to test the connection to narrow down the source of the problem. Another extremely valuable diagnostic tool is the multimeter. Like the test light, this electrician's tool tests for current, but it provides a great deal more information. It has a variety of settings to measure AC (alternating current) or DC (direct current) voltage as well as ohms -- the measure of electrical resistance or continuity. Multimeters also have a digital or analog (needle indicator) readout that displays the amount of voltage flowing through. In this way, you can test a power source, and check to see whether an electrical component or switch is receiving the proper amount of power. For example, to check our vehicle's battery to make sure that the power source is good, we set the multimeter to DC current and an approximate voltage of 20 volts. We then connected the multimeter's the positive (red) probe to the positive terminal of the battery, and the negative (black) probe to negative (figure D). With a functional 12-volt battery, and with the vehicle's motor turned off, the voltage readout should be about 12 volts (figure E). To test the alternator, we simply leave the multimeter connected in the same fashion and start the vehicle and check the readout once again. With the car running, the readout should be slightly above 12 volts (figure F), indicating that the alternator is charging the battery. Multimeters can also be used to test fuses. The multimeter used in our demonstration utilizes a continuity feature that gives an audible signal when the positive and negative probes are touched together (figure G) or when the probes come into contact with either end of an unbroken electrical wire. Continuity simply means that electrical current is able to flow continuously through a particular circuit or span of electrical wiring. A properly working fuse has a continuous filament running through it (figure H) and should allow current to flow through. Using the continuity feature feature, and connecting a probe to each post of the fuse, you may test to see whether current can flow through the fuse in question (figure I). With the meter hooked up in this way, a functional fuse will be indicated by the audible tone. Note: Multimeters perform a variety of diagnostic tests, and there may be differences in the capabilities and operating features among different brands and models. Read and follow any instructions that come with your model.
RESOURCES :
Auto Repair for Dummies
Author: Deanna Sclar
ISBN: 0764550896
Some vehicles provided by Beaty Chevrolet
Beaty Chevrolet
9615 Parkside Drive
Knoxville, TN 37922
Phone: 865-693-7712
Web site: beatychevrolet.com
Some vehicles provided by Ted Russell Ford
Ted Russell Ford
8551 Kingston Pike
Knoxville, TN 37919
Phone: 865-693-7611
Web site: www.tedrussell.com
The Haynes Automotive Tools Manual : The Haynes Manual for Buying and Using Automotive Tools
Model: 1563921073
Author: Eric Godfrey and John H. Haynes
(1994)
To order this title from Amazon.com, click here.
Haynes Publications
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