Your car's electrical system runs because of some essential components including: a battery, fuses, and an alternator. When any one of these components fail, your car will not run or it will perform poorly. Unfortunately, it is not always apparent which part is giving you the trouble. We'll examine each component, discuss its unique characteristics, and outline simple maintenance options to help you make the proper diagnosis.
1. Alternators. Car alternator problems are usually noticed when you realize the juice to your headlights has been reduced. No longer can you see hundreds of feet in front of you, instead the light barely makes it past the front bumper. Check the wires leading to the alternator and make sure that they are secure and free of corrosion. Examine your alternator belt for cracks as well as for tension. If your headlights are still dim, then it is likely your alternator will have to be replaced. Do not put it off as the alternator can drain your battery.
2. Batteries. If your car will not start, your battery may be to blame. Most cars come equipped with sealed, maintenance free batteries. Still, "maintenance free" is not an entirely correct design as corrosion can build up on the terminals causing an otherwise fine working battery to fail. Remove the cables, clean with a wire brush, and reattach the cables. Apply lubricant to each terminal to limit future corrosion. If your car's battery is not "maintenance free" add distilled water to each cell as needed. Use a good set of jumper cables to get your car started. If the car still will not start the battery is either completely shot or the starter or solenoid [relay] are not working. Battery life varies depending on what type of battery is in your car and usage; consider replacing your battery every 3-5 years before problems arise.
3. Fuses. Your dash lights may be working, while your left rear blinker has failed. If that is the case, it is likely your electrical problems are with the fuses. You can pull off the fuse panel [usually located under the dashboard] and check to see which fuse has burned out. Today's cars use transparent blade style fuses that are rectangular in shape. Observe each fuse and see if the internal wire has burned out. You can find the fuse fast if the auto manufacturer has labeled each one by circuit. If not, you will have to determine by a process of elimination which fuse has failed and replace it.
Batteries and fuses are readily available at auto supply stores and most will carry a selection of alternators too. If you find prices for your Ford alternator or BMW alternator are too high, you can save lots of money on original equipment manufactured parts with some of the reputable online providers. Shop with those retailers who have the widest selection of inventory, the best prices, and the most favorable shipping and return policies.