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Summary
  • A wiring schematic or diagram contains symbols representing the wiring and electrical components.
  • It pays to know your tools, learn how to locate a short circuit, and familiarize yourself with the circuit troubleshooting procedure.
  • An electrical component will only work if it has both power and ground. Also, a device with no power almost always translates to an open power side, such as a blown fuse.

Dealing with mechanical issues like replacing a flat tire is one thing, but addressing a car’s electrical system and troubleshooting it effectively is an entirely different story.

In this guide, we’ll tell you all the things you need for a successful electrical troubleshooting job.

Know Your Tools

Having the right tools is crucial to an effective troubleshooting job. In the case of electrical problems, it can be quite difficult to identify the problematic area at first glance.

Unlike mechanical issues where you need to look out for rust, wear, and other visible signs of damage, electrical problems usually require you to be more observant.

Electrical troubleshooting requires a specific set of tools, depending on what type of problem you’re dealing with.

Fused Jumper Wire

A fused jumper wire, also known as a test lead, is used to supply power or ground to a circuit. It can also bypass a switch to check a circuit.

A fused jumper wire is a simple device that contains a fuse, a pair of alligator clip ends, and an insulated wire. If an electrical component isn’t working, you can use this wire to supply temporary power and/or ground to its circuit.

Keep in mind, however, that a fused jumper wire should never be used to bypass any resistance or load in a circuit. Doing so could result in a blown fuse on the jumper lead.

diagram of how to check car ground
Diagram showing how to check a ground | Image Source: Richard McCuistian

Test Light

A test light is another simple device that consists of a bulb with a probe and ground. It’s usually used to detect battery voltage potential. You can check for power with the test light’s cable clip connected to the battery negative or ground (check your light on a known good power source first).

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You also need to know the power of the “dark side,” which is the ground. You connect the test light cable clip to the positive side of the battery and check for ground, which is just as important.

, Electrical Troubleshooting Tips for the Dedicated DIYer

Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.

Pro Tip: An electrical circuit is basically a loop, and if that loop is broken anywhere the circuit won’t work. If there’s resistance, it may work but not very well.

This device is usually labeled as a “12-volt” test light and shouldn’t be confused with a test light for household current, which holds around 110 to 220 volts. 

A test light can generally check two things: electrical power and grounds. 

If the bulb on the test light turns on, it means that there’s enough power. However, that doesn’t indicate that the power is enough to operate an electrical load.

, Electrical Troubleshooting Tips for the Dedicated DIYer

Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.

Pro Tip: This is why it’s good to have a headlight bulb mounted in a clear bottle (like a large baby food jar) so you can check for power and ground using the headlight bulb rather than a test light, which will illuminate with only a small amount of current.

To check for grounds, link the tip of the test light to the ground wire. An illuminated test light indicates that there’s a ground connection.

guide for electrical ground troubleshooting
Fuse removed, key off. If the load is good and the ground is good, the light will illuminate. If not, suspect the load or ground. | Image Source: Richard McCuistian

Logic Probe

A logic probe is a diagnostic tool that can differentiate between high and low voltage levels but pulls no current at all.

The logic probe usually emits a red light if it touches the battery voltage and a green light if the probe is touched to ground.

Most logic probes emit an amber light when they detect a change in voltage levels.

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Some probes also flash a red light upon detecting a pulsing voltage signal and a green light upon detecting a pulsing ground signal.

When using a logic probe, always make sure that it’s connected to a power and ground source like the battery.

Digital Multimeter

A digital multimeter is a type of high-impedance test meter that measures any automotive circuit within its range. It pulls no current but most DVOMs do have an AMPS function so you can connect the meter in series with a load of up to 10 amps. These meters will have an internal fuse.

Common configurations of digital multimeters include a voltmeter, ohmmeter, and ammeter.

It pulls no current but most Digital Volt & Ohmmeter (DVOMs) do have an AMPS function so you can connect the meter in series with a load of up to 10 amps. These meters will have an internal fuse.

Richard McCuistian, ASE Certified Master Automobile Technician

Oscilloscope

An oscilloscope is a visual voltmeter that displays voltage changes. This device comes in two types, namely digital and analog.

Get to Know Wiring Schematics

If you’re a DIYer, you’ll probably need to level up your automotive knowledge bank when it comes to electrical troubleshooting.

Aside from learning terminologies and system locations, you’ll also need to understand various wiring schematics and symbols.

1987 schematic of vehicle wiring
This wiring schematic is from 1987. Wiring schematics change from year to year and vehicle to vehicle. There are dozens of different types of wiring schematics. | Image Source: Richard McCuistian

Most service manuals include wiring schematics of every electrical circuit in a vehicle. Also referred to as a diagram, a wiring schematic contains symbols representing the wiring and electrical components.

All schematics basically contain the following:

  • Power-side wiring of the circuit
  • Splices and connectors
  • Wire sizes and colors
  • Trace color
  • Circuit number
  • Electrical components
  • Ground return paths
  • Fuses and switches

Learn How to Locate a Short Circuit

A short circuit is one of the most common electrical issues that can happen to most vehicles. This problem usually blows a fuse and its replacement in an attempt to locate the trouble area.

A short circuit is an electrical connection to another wire or to ground before the current flows through some or all of the resistance in the circuit. In most cases, a short circuit involves a wire on the power side of the circuit coming into contact with metal.

There are more than five ways to locate a short circuit, but we’ll only go through three of them.

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Gauss Gauge Method

A Gauss gauge is a handheld tester that responds to weak magnetic fields that come from an intermittent current flow. It will detect the weak magnetic field and display the results through the needle gauge.

Circuit Breaker Method

For the circuit breaker method, you’ll need to hook up an automotive circuit breaker to the fuse holder contacts using alligator clips.

The circuit breaker will open and close the circuit alternately, and protect the wiring from heat damage.

guide for car light, breaker, and breaker cycle
With the tool in place and the circuit energized, the breaker will cycle and the light will be on when the breaker is open. | Image Source: Richard McCuistian
hand holding a car circuit breaker
Use a circuit breaker as near to the fuse classification as possible to prevent damage to the circuit. | Image Source: Richard McCuistian

Ohmmeter Method

The ohmmeter method is a highly recommended procedure when finding a short circuit. This is because the device is capable of displaying low ohms when a short circuit is present.

An ohmmeter will usually read zero or almost zero ohms if the circuit is shorted.

Circuit Troubleshooting Procedure

When troubleshooting wiring problems, the first thing you need to do is verify the malfunction while the key is in the ignition. Also, make sure that the gear is in reverse, and check for the operation of the backup lights. When checking connectors in a circuit you’re troubleshooting, check the ones that are easiest to access first and eliminate those.

Check every component and identify which ones aren’t working as they should. Then, check the fuse for the backup lights, and check for voltage at the backup light socket using a voltmeter.

If no voltage is available at the socket, consult the proper wiring diagram.

The Basics of Electrical Troubleshooting

Here are crucial details to help you on your electrical troubleshooting task:

  • An electrical component will only work if it has both power and ground.
  • A device with no power almost always translates to an open power side, such as a blown fuse.
  • Power on both sides of a device means there is an open ground.
  • A blown fuse usually means that there’s a grounded power side wire.
  • Most electrical faults result from heat or movement.
About The Authors
Written By Automotive and Tech Writers

The CarParts.com Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by CarParts.com's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Reviewed By Technical Reviewer at CarParts.com

Richard McCuistian has worked for nearly 50 years in the automotive field as a professional technician, an instructor, and a freelance automotive writer for Motor Age, ACtion magazine, Power Stroke Registry, and others. Richard is ASE certified for more than 30 years in 10 categories, including L1 Advanced Engine Performance and Light Vehicle Diesel.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

File Under : Electrical System , DIY Tagged With : ,
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