Automotive Electrical Troubleshooting Tips

Automotive Electrical Troubleshooting

In the late 80’s and early 90’s electrical systems used to be simple. Electrical powered items in cars have been around quite a while, however computer controlled safety controls and convenience items are becoming the standard in automotive systems technologies. Today’s electrical systems are a major part of automotive maintenance and repair.

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Many technicians find automotive electrical troubleshooting a daunting task. Its not hard when you master the basics.These are some basic electrical systems for troubleshooting:

• Battery

• The starting system

• And the Charging system

• Lighting

• Windows

• Locks

• Fuel systems

• Seats

• Ignition systems

Several diagnostic tools these days can assist in pinpointing the component or module that’s causing any faults or errors. Verify if possible which modules or components are working properly then inspect for continuity in the system you are working on.

Aluminum is pretty much the major metal used in vehicle construction these days. All manufactures understand its’ superb qualities like: weight to strength ratio, durability, and flexibility.

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Although aluminum has good corrosion resistance properties, corrosion is always at work in and around the metal surfaces. Many times the ground points are a problem for mechanics when performing automotive electrical troubleshooting. Electrical systems with vehicles within aluminum bodies or frames. Be sure to check all grounds and connectors in question for condition, corrosion or electrolysis.

In many cases all of theses systems will be receiving battery power. After verifying that the battery is healthy and charged (If not, correct battery condition) then proceed with further testing. As mentioned before perform an electrical test for any faults or codes that may be stored.


6 Basics for automotive electrical troubleshooting -

1. Power - is it available and how is the battery condition

2. Protection - fuses, and relays etc.

3. Consumer(s) - what is using the power?

4. Controller(s) - what is directing the power where needed?

5. Positive - hot

6. Negative - ground

Checking all of these will usually show you where your problem lies.

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Battery Charging and Testing:

Often automotive electrical troubleshooting starts with the main power source. The battery (or in some cars; batteries) is the main power source for the automotive electrical system. These are 3 of its major duties:

1. Provide electrical power to start the engine.

2. Stabilize the voltage in the automobiles electrical system

3. Supply limited power to accessories when alternator power is incapable or unavailable.

Many batteries today are rechargeable; know the correct Cold Cranking Amps and the type/size of battery to be charged or tested before charging and testing.

REMEMBER: Always use safety glasses when handling automotive batteries

• Always check the level of charge when troubleshooting electrical systems. Get used to testing the battery for typical conditions: low voltage can cause faults in the system.

• When testing the battery run the proper test for battery size and type.

• If charging is required, we recommend slow charging if time permits

• Check and repair or replace battery cables if required (frayed or damaged cables can cause voltage drops). Connections should be secured properly.

• If the battery tests ok but will not hold a charge suspect starting circuit and charging circuit. Test these systems as required.

Starter System testing and troubleshooting

Most starter issues can be resolved by checking the following:

• First be sure the battery is in good condition

• The starter condition, wiring and connections. Does it crank or does it crank slowly? If so, the problem is usually in the starter itself or the solenoid.

• Listen to the starter while cranking; is it noisy, does it engage or does it disengage? If these are the symptoms then the starter is the problem.

• If the battery is in good shape, and the engine will turn by hand, the starter is the main suspect. Just to be sure, make these 3 voltage drop checks:

1. Voltage drop between the frame and the negative post (not the clamp) If excessive; clean connections and replace faulty cables

2. Voltage drop between the car frame and the starter frame If excessive; remove starter and clean both surfaces

3. Voltage drop between battery positive terminal and starter (+) terminal If excessive; thoroughly inspect cables and replace faulty cables

Automotive electrical troubleshooting charging systems

The charging system on many vehicles consists of 3 major components:

1. The battery or batteries

2. The alternator

3. And the voltage regulator

The alternators on vehicles are needed to supplement and restore the electrical power given from the battery. Two regular problems most technicians are faced with regarding the charging system are overcharging and undercharging. Many charging system problems can be caused by; a bad battery, a worn belt or belt pulley, a faulty alternator, or bad connections or cables.

Keep in mind that the vehicle that you are testing may ONLY have a problem that appears when operating at a particular temperature. Be thorough and test through different temperature ranges. The alternator output can be checked in many ways. There are numerous manufacturing variations for automotive charging systems. That’s why it important to have the proper manufacturers service information.


Find out if the alternator is producing the correct voltage to support the battery and maintain charging, and if it is producing the correct amperage according to its rating. These tests can be done with a multimeter, or with other alternator test equipment.

Using your meter:

Working around electrical systems can be dangerous, so always practice safety. Use your multimeter as much as possible. The more you use this instrument the better automotive technician/mechanic you will become. Most of the electrical testing and troubleshooting on vehicles can be done with a multimeter.

ALWAYS use caution and never assume the power is off in a circuit, ALWAYS be sure. Use the basics mentioned above for checking most of your electrical circuits and equipment.

Checking, testing, and troubleshooting electrical components:

Take quick and simple resistance and continuity measurements with your multimeter. This will save you time and boost your income. Here are some components that can be quickly tested with your meter: switches, horns, relays, heater fans, cigarette lighter, fuses, lights, starter, alternator, sound systems etc.

Here are a few more tips for automotive electrical troubleshooting:

• Continuity check (see schematic or diagram for routing)

• Checking related grounds - are they loose, corroded, or is the paint an issue

• Voltage drops – try finding drops by dividing the vehicle into sections

Review all wiring diagrams and schematics thoroughly.

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