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A Handy Guide to Troubleshooting Common Car Electrical Problems

Troubleshooting Car Electrical Problems
Fixing electrical problems is a skill that every car owner must possess. You need not run to the mechanic for minor issues. It is a simple and straightforward job. Go through this quick primer on solving electrical problems in your automobile, to get an overview of the procedure.
Omkar Phatak
Last Updated: Sep 25, 2017
When Should the Battery be Replaced?
The average life of any automobile battery is three to seven years. It makes sense to replace it after 4 years of service, to maintain optimum efficiency.
To solve a car's electrical problems, all you need is a fundamental understanding of the Ohm's law and a detailed diagram of its electrical circuitry. The circuit serves as the control and powering mechanism for all its working systems. Using a voltmeter and by checking for continuity, you can solve most of the problems. Almost every system in a car needs an impetus through the current supplied by the battery, making it the prime mover of sorts. The battery's depleted charge level is constantly replenished by the alternator. Ergo, any problem with the power system can be traced to the battery, alternator, or its connecting mechanism.
Here are some of the signs that indicate a probable electrical system issue with a car.
  • It doesn't start.
  • You hear a clicking sound but the car doesn't start.
  • Headlights tend to be dim.
  • Battery light comes on.

In most of these cases, the problem lies with the battery or the alternator.
The typical voltage range in a car's electric circuitry is around 10 V to 16 V. Therefore, experiencing an electric shock is an unlikely scenario unless you are tampering with the ignition assembly or the battery system of a hybrid car.
Man disconnecting wires of car
Refer circuit diagram of the electric assembly before disconnecting any wires or making new connections. Check and keep track of the colors of the wires and keep in mind, which one goes where. Disconnect the battery when replacing or removing any electrical components. This eliminates the risk of any components being inadvertently shorted and the PCM (Power train Control Module) getting damaged.
Diagnostic Principles and Tools
Digital voltmeter
The diagnostic tools needed for troubleshooting are an ohmmeter to measure resistance and a voltmeter with attached leads (or a multimeter that serves both these functions), besides a discerning intellect. You may also use a 12 volt light tester for a quick check but it's better to have a voltmeter or a multimeter to get accurate readings.
The principle for diagnosing an electric problem is the Ohm's law (V = IR). Voltage is directly proportional to current, for a solid conductor and the proportionality constant is the resistance of the circuit.

Remember that every device needs electric power for its functioning and there is a minimum threshold voltage, that is absolutely necessary for its operation. Ergo, the diagnostic method is simply measuring the voltages at various load points of the car.

Load points are contact points, where power is supplied to a load, which could be the car light bulb, the windshield wiper, the ignition assembly, or any other working car part, which has problems. Therefore, if the voltage levels at any of these points are abnormal, it is definitely indicative of an underlying problem. Thus, most electrical problems are essentially low voltage, 'no voltage', excess resistance, or circuit discontinuity problems. In some cases, the culprits might also be some burned out components.
Check the Battery
Man removing battery from car
The first place to check for electrical problems is the car battery. If the battery itself is not providing the required output voltage, then every component associated with it, has issues. So to check the battery output first, disconnect it from the car connections. The PCM may get reset and lose its programmed settings, when the battery power is disconnected. So attach a 9 V battery to the PCM, to avoid this.
Then, measure the voltages between the output leads of the battery. If the voltage reading is equal to or in excess of 12.43 V, your battery is charged sufficiently enough and is working. If the voltage is around 12.66 volts, your battery is fully charged and you have no reason to worry. If it is less than 12.43 V, the battery needs charging. If the battery happens to be older than four years, it is best to get it replaced, as it might already have crossed its peak-functioning lifespan.
Test Alternator Functioning
Man checking car function with voltmeter
If the battery voltage levels are fine, the problem might be with the alternator. To check whether this is indeed the case, arm yourself with a voltmeter and connect its leads to the alternator output terminals.
Now start the car and make raise the RPM levels of the engine. Observe the alternator voltage output reading. It should be in the range of 13 V to more than 14 V. If the engine is functioning around 2000 RPM or more, the alternator is fine. However, if the voltage level has plunged well below 13 V, it is most likely that the alternator has a problem. Get the device checked for a loose belt or any other kind of mechanical malfunctioning, that it may have suffered. It is best to get it replaced, to be on the safer side.
Check Voltage at Load Points
Man tightening terminals of car battery
Next, reconnect the battery and check the voltage at load points of the devices, which are not working properly. If the voltage is zero or very low at a particular point, there are many possible case scenarios. One possibility is that the fuse that protects the device has burned out or secondly, the relay that switches power to that part has stopped working. Check and replace these, if you find them to be faulty.
Check the Grounding
Next, check the grounding at that point. The car circuitry is grounded in its metal body itself. If the grounding is at fault, current conduction is not possible. If that is the problem, then fix it by grounding the terminal from that point.
Look For Corroded and Disconnected Wires
Man checking wires of car
If the fuses are in place, grounding is sound, and the relays are working properly, then a third reason for the low or zero voltage could be corroded wires or wires with discontinuities. Checking for corroded wires can be done by checking the voltage drop across them. If the voltage difference between two connected points of the wire shows a voltage drop of more than 0.1 V, there is a problem. You must replace it. The method for checking continuity is to measure the resistance between the points, connected by the wire, using an ohmmeter. If it's infinite, the wire has broken inside and must be replaced.
Verify End Device Problem
If neither the fuses, relays, or wires show a problem and the devices are not working, then you can safely conclude that there is problem with the end device. Water exposure of an electric circuit can lead to such shorting of devices. Water seepage into windshield wiper circuitry or other circuitry is common during the rainy season.
Studying the wiring diagram carefully will help you figure out complex electrical issues. Performing a periodic check of the car's electrical installations in this way, prevents any future problems that may crop up. Changing, replacing components, and engaging in full-scale car repair could be a job, best left to a mechanic but understanding and diagnosing the problem on your own, is easily possible.