The battery itself should be at least 70 percent charged and read If the battery is low, it should be recharged and tested.
The output of the charging system should also be checked, and be about 1. If the battery is OK, your voltmeter should read within 1 volt of battery voltage at the circuit load point in any given circuit. Low circuit voltage is usually caused by excessive resistance at some point in the wiring.
Usually this means a loose or corroded connector, a faulty switch or relay or poor ground. To find the point of high resistance, use your voltmeter to do a "voltage drop test" at various points throughout the circuit. If the voltmeter shows a drop of more than a 0. Ideally, the voltage drop should be no more than 0. Loose or corroded battery cables and ground straps are a common cause of voltage-related problems. Sometimes undersized wiring can cause low voltage.
It is not something you will find in many original equipment wiring circuits, but it is a common mistake that is made in many do-it-yourself wiring installations for aftermarket accessories.
The higher the amp load in the circuit, the larger the required gauge size for the wiring. Every electrical circuit requires a complete circuit to operate.
Voltage to the load will not do any good unless there is also a complete ground path to the battery. The ground path in the case of all metal-bodied cars is the body itself. In plastic-bodied cars, a separate ground wire is needed to link the load to the chassis. In either case, a poor ground connection has the same effect as an open switch.
The circuit is not complete so current does not flow. To check wiring continuity, you need an ohmmeter or a self-powered test light. An ohmmeter is the better choice because it displays the exact amount of resistance between any two test points. A test light, on the other hand, will glow when there is continuity but the intensity of the bulb may vary depending on the amount of resistance in the circuit.
But it is OK for making quick checks. Never use an ohmmeter to check resistance in a live circuit. Make sure there is no voltage in the circuit by disconnecting it from its power source, by pulling the fuse or by testing downstream from the circuit switch or relay. Ohmmeters cannot handle normal battery voltage and, should you accidentally complete a circuit through the meter, you may damage your meter.
Ohmmeters are great for measuring circuit resistance but you have to use care when checking electronic components. An ohmmeter works by applying a small voltage through its test leads, and this voltage can be enough to damage some electronic components such as the oxygen sensor. Special high impedance 10, mega-ohmmeters should be used for electronics testing.
Tracing wires is not as easy as it looks because the circuit wire will sometimes change color after passing through a connector, switch or relay. Always refer to a wiring diagram when possible. This way you will know how the wires are routed and what colors are used. Now that we have covered some basic troubleshooting techniques, what is the best way to find an electrical fault fast?
It depends on the nature of the problem. For a "dead" circuit, the first thing to look for is voltage at the load point. Use your voltmeter or volt test light to check for voltage. If there is voltage, the problem is either a bad ground connection or the component itself has failed. Check the ground connection with your ohmmeter. If the ground connection is good, the fault is inside the component. If there is no voltage in the "hot" wire to the component, then the problem is in the wiring.
Trace back through the fuse panel or relay or circuit breaker until you find voltage. Now look for an open or short that is preventing the current from reaching its correct destination. Next comes bad connections. The resistance created by a loose or corroded connection will cause a voltage drop that can have an adverse effect on circuit components.
An ohmmeter can be used to check non-powered circuit connections for excess resistance, but a better method is to use a voltmeter to check for a voltage drop across a connection. The voltmeter leads are connected on either side of the circuit component or connection that is being tested.
If a connection is loose or corroded, it will create resistance and produce a reading on the voltmeter. As stated earlier, a voltage drop of more than 0.
For more information about voltage drop testing, Click Here. The worst kind of electrical problem to troubleshoot is an intermittent one. Everything works fine in the shop but as soon as the customer gets the car back it starts to act up again. An intermittent open or short is usually the result of something heating up and breaking or making contact, or something that is loose and is making periodic contact.
Loose or corroded connections and switches are often responsible for this kind of problem, so try jiggling the wires and circuit switch to see if it changes circuit voltage or resistance. A wire that is rubbing and has chaffed away some of its insulation can make intermittent contact causing a short, so again wiggling suspicious wires will often reveal the problem. Perform another road test and make sure everything is fine before delivering the car back to the client.
The following section contains techniques to help you recreate an intermittent problem so you can test the defective system. Vibration may cause intermittent electrical problems. This is probably the worst-case scenario and such problems are sometimes really hard to troubleshoot. In the meantime, following a general procedure like the one that follows is probably your best bet.
Locate the connectors and wiring harness related to the electrical system you are inspecting. Grab the harness with one hand and shake it in all direction and watch if the symptoms appear. Inspect the wires for damages. Connectors that are exposed to water or moisture can develop a thin film of corrosion on the connector terminals. Always make sure to disconnect suspected connectors as the corrosion may not be visible from the outside.
When in doubt, cleaning the connector with electrical connector cleaner might help. Whenever suspecting a problem located under the hood, always start by inspecting the ground connections. A good ground is the base of all electrical circuit. Improperly routed or improperly clamped harness can become pinched during the manufacturing or later in the life on the vehicle when aftermarket accessories are installed.
Vibrations coming from the vehicle can aggravate a harness or wiring running along with metal brackets. Inspect the wiring for damages near the metal parts of the seats. To determine if an electrical problem is related to heat, use a heat gun to heat the suspected part while monitoring the electrical system. If the problem only happens in cold weather or if the customer mentions that the problem goes away after the car warms up, it may be related to water freezing somewhere in the electrical system.
The best method to check for this is to have for the client leave his car for the night if the expected weather is cold enough to create the incident. Let the car outside and inspect it again the next morning. If you are courageous enough, you can even try to perform the preliminary checkup and start the troubleshooting process outside to keep the car cold for long enough for you to identify where the problem is coming from.
To make the process as simple as possible, make sure you have all the information on the system to be tested before you begin. Correctly understanding the system operation is also critical to reach a correct diagnosis. Whenever testing an electrical circuit, having access to the wiring diagram can make a world of difference. Electrical systems are more complicated now than ever and all cars are built differently. Trying to diagnose an electrical problem without a wiring diagram is basically like trying to find a needle in a haystack.
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