Vehicle Electrical Systems

Summer heat can be just as damaging as winter’s cold temperatures to a vehicle’s electrical system. Conducting some simple checks and maintenance steps will help fend off future problems and ensure that the electrical system functions properly and maintains a high level of operating efficiency.

There are four fundamental elements to a vehicle’s electrical system, and all must properly work together.

  • Batteries: The batteries provide power for engine cranking and electrical loads when the alternator is not generating power, and also stabilize voltage levels in the electrical system.
  • Alternator: The alternator generates power for all of the vehicle’s electrical loads while the engine is running. This includes the engine’s electronic controls, headlights, etc. The alternator also recharges the batteries after cranking the engine or using the vehicle’s electrical devices while the engine is off.
  • Starter Motor: The starter motor converts electrical energy into mechanical energy needed for cranking the engine over.
  • Wiring: There are two wiring subsystems related to the charging and cranking circuits. One supplies power from batteries to starter motor. This includes wires that are large enough to transmit several hundred amperes during cranking, and transmit power back to batteries from the alternator for charging.

The second subsystem transmits power from the alternator to the batteries for charging, and is usually connected from the alternator to the starter.

There is also a control circuit that transmits power to the starter’s solenoid. This includes the key switch and associated wiring.


Technicians should be reminded to always follow the recommended safety practices whenever performing work on a vehicle’s electrical system. These include:

  • Wearing face, eye and hand protection.
  • Being aware of moving parts, such as belts, fans and pulleys, as the engine will be running during testing.
  • Setting the parking brake.
  • Shifting the transmission into neutral position.


Preventive maintenance goes a long way toward prolonging battery life. The following tips, which aren’t just for springtime, should be done every time the battery box is opened.

Do a general visual inspection. Is the battery firmly mounted in the battery box? Do any of the batteries have cracked cases or noticeable bulging of the sides?

Are the cables secured firmly to the battery? Are there loose or corroded cables?

If the main battery cables are “green,” there is corrosion and resistance, which leads to poor starter performance.

Any problems observed should be fixed right away before they become a road call.

When the battery box is open, you should be able to clearly see the writing on each battery. If you don’t, get out a rag and wipe off the top of each battery. Salt and common dirt, combined with moisture, can create an ionic solution capable of forming a current path on the top of the battery.

This 30-second step reduces the opportunity for parasitic current draw (drained batteries) and corroded battery terminals.

While the battery cover is off, also check the battery state of charge and health. Check with the battery manufacturer for its recommended method of testing - electronic tester, carbon pile load tester, etc.

This step isn’t necessary every time the battery cover is off, but it is a good idea to perform this periodically.

Also, while changing the engine oil during engine service, visually inspect the batteries and cables.

Remember to check with your battery suppliers for their recommended interval between testing batteries.


When inspecting the starter and alternator, keep an eye out for terminal corrosion, loose connections and damaged connections. Also make sure both components are securely mounted in place.

Generally, if you have not had charge/start problems on a vehicle over the winter, there is no need to take the time to disassemble connections or perform voltage/cable drop tests. If there is salt or dirt build-up on the terminals, it should be removed to prevent future corrosion.

This should be limited to wiping components down or wire-brushing terminals on the alternator and battery connections. These components may not react favorably to pressure washing.

Water can be used to remove salt or dirt from the starter. Use the lowest pressure possible to get the job done, as this prevents moisture from becoming trapped in areas of the vehicle from which it can’t drain or evaporate.

A soft brush or rag combined with low-pressure water is the best choice. We’re removing salt and dirt here - not graffiti from concrete.

Once the terminals are clean, dry and verified to be corrosion-free, a high-quality corrosion-inhibiting grease should be applied. Remember to apply the grease after tightening any terminals you may have removed. Corrosion-inhibiting grease is often a dielectric, so you don’t want it getting between the terminals.


Problems with a vehicle’s electrical system are often misdiagnosed as a starter or alternator problem. A significant number of products returned to Mitsubishi Electric Automotive America under warranty and deemed “defective” by the customer are found to be “NTF” (No Trouble Found).

When experiencing trouble with the electrical system, it is best to take a systematic approach to troubleshooting the problem: batteries first, wiring and connections next, and finally the starter or alternator. Keep in mind that it is not always an electrical component that is the problem. Vehicle wiring needs to be checked as well.

Proper diagnosis consists of three basic questions:

  • What are the symptoms? Basic observations seen, heard, felt or smelled.
  • What has caused the symptoms? Using proper diagnostic tools will help identify the cause of the electrical system problem or failure.
  • How is the problem fixed? This step involves part repair, replacement or adjustment.

Eric Karr is an account manager and Danny Ritter is a technical support manager for Mitsubishi Electric Automotive America – Heavy Duty Division. Based in Mason, OH, Mitsubishi Electric Automotive America, a U.S. subsidiary of Mitsubishi Electric Corporation, is a leading manufacturer and supplier of customized powertrain, body and chassis products and in-vehicle entertainment and navigation systems.