Get To Know Your Mercedes’ Electrical System

Modern Mercedes-Benz cars and SUVs are engineered with complex electrical systems that include a number of interconnected computers, fiber optic links and data busses. Onboard systems requiring electrical power include the starter and spark plugs, anti-lock brakes and electronic stability control. Electricity also powers the heating and air conditioning as well as the vehicle security and infotainment systems. The circuits are controlled by relays, fuses and switches. The battery provides the initial power to start the vehicle. Once the motor is running, the alternator assumes the electrical load. If one or more components in the electrical system fail, your car may not start or run correctly.

While troubleshooting an electrical problem is typically performed with cutting-edge test equipment, some basic issues still arise that can be solved using old-school skills. It is important to know a few basic troubleshooting techniques in case your lights, wipers, heater fan or air conditioning stop working. This will enable you to safely operate your CLA, SLK or ML250 in the snow or rain during your daily commute or weekend getaway to the Cape.

Dead Battery or Bad Battery Terminals

The electrical system in your Mercedes is a closed circuit that requires an independent power source, which is supplied by the battery. Cold weather like that which occurs in Massachusetts during the winter is especially hard on car batteries. The strength of the battery will drop along with the plummeting temperatures. While a battery loses more than 30 percent of its power at 32 degrees, this loss increases to 60 percent when the thermometer dips below zero. Starting a car in the winter can require twice the amount of cranking power needed during the summer. The high temperatures of August can also shorten the life of your battery. As a result, it is important when troubleshooting an electrical system to ensure that the battery is up to the task. Install a battery with sufficient cold cranking amps that can also handle the heat of summer. When checking the battery, ensure that the terminals are free of corrosion and the clamps are firmly connected. Loose battery cables and corrosion also rob your battery of cold cranking power.

Malfunctioning Alternator

While the winter is notoriously hard on batteries, it can also be tough on your alternator and car’s charging system. On a warm day, the alternator can fully recharge the battery in approximately 20 minutes of driving. In cold weather, it will need more time to compensate for the added strain on your battery. You may have to step on the gas and rev the engine to begin the charging process. If you hear a squeal from the alternator drive belt, it is not gripping tightly. It can slip because the cold weather has stiffened the belt material. As a result, the alternator is not sufficiently charging the battery or producing enough power for your electrical system. Having to recharge the battery during the winter can place a strain on your alternator. Warning signs that your alternator is failing includes dim lights, failure of a new battery to stay charged or stalling at a red light. While your car may start with a bad alternator, it will not run properly for an extended period. Each Mercedes automobile is engineered to function with a specific type and size alternator. Mercedes OEM parts are made from high-grade material to the exact specs required by the factory. As a result, OEM Mercedes parts will fit and function properly without the need for special adjustments or extra parts. Adherence to the original specs will save you time and money.

Blown Fuse

While shorts or open circuits can be difficult to isolate, a blown fuse or relay is the likely problem when the wipers, defroster or lights fail to work. This is usually the issue when a single accessory, light or other electrical or electronic component stops working. Fuses and relays are simple to diagnose, find and replace. Check your owner’s manual for the location of the fuse panel controlling that component. Your car or SUV may have more than one fuse box mounted in different areas of the vehicle, including under the dashboard or inside the engine compartment. Use a fuse puller to remove the fuse from the panel. The tool resembles a pair of small plastic tweezers. Hold the fuse up to the light. If the metal piece in the middle is broken, the fuse is bad and has to be replaced. Ensure that you install a new fuse with the same rating. If the fuse is in good condition or blows again, you may have an electrical short. Replacement fuses are available in packs that contain several popular sizes. Keep one of these kits in your car for emergencies.

Faulty Switch

You should test the suspected faulty switch in all possible positions to determine whether the accessory actually works. Inspect the switch for loose connections. Determine if the switch has a built-in circuit breaker. Consult your owner’s manual or repair guide for the steps needed to reset the breaker.

Wiring Short Circuit

A complex network of wires runs through your car or SUV. Before you try to repair an electrical short, ensure that you check other potential reasons for the issue. The reason that your taillight may not be working could simply be a burned-out bulb. Electricity flows in only one direction from the battery and through the system. While components will not work without electricity, they may also fail to operate if the electricity is flowing in the wrong direction. A damaged, disconnected or incorrect wire can cause a short circuit. While most car service manuals include a color-coded wiring diagram, it can be difficult to follow when trying to trace an individual wire. In some cases, it may be easier to replace a wiring harness. Some modern vehicles are replacing wiring with printed circuits to make installation and repair much simpler.

A healthy electrical system is essential for a safe reliable ride. If left unchecked, a weak or dead battery, a malfunctioning alternator or an electrical short can wreak havoc with other electrical system components. If your vehicle’s electrical system is malfunctioning, you can rely on to have the OEM Mercedes-Benz parts that you need for the safe and smooth operation of your car or SUV. You can search our extensive catalog by part number, VIN or keyword. Alternatively, you can select the correct year, make and model from the drop-down menu. Our trained parts specialists are also on hand to answer any questions and ensure you’re ordering the right part for your Mercedes vehicle.