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Electrical System Problems

by Aaron Turpen

For most DIY mechanics, nothing is as frustrating as electrical system problems. The tools a professional shop will have to diagnose them are sophisticated and costly and most home mechanics don't have them. Many electrical problems can be solved in the garage, however, without resorting to costly repairs at the shop.

Safety Note

While there is little danger of being shocked by your car's 12V DC system, the danger is still there. Especially when working on the high voltage starting system and the systems on some accessory units on modern cars. This is especially true of hybrid and electric cars. So use proper safety equipment and precautions when dealing with your vehicle's electrical system. Always disconnect the battery's ground wire when pulling or replacing electrical parts. Finally, never replace a fuse with a larger fuse to "fix" a problem - this leads only to more problems.

Keep It Simple Stupid

The KISS principle is alive and well in auto mechanics and quite often ignored. If you're having an electrical system problem, check the simple stuff first.

  • Is the battery fully charged?
  • Is everything plugged in?
  • Are the fuses intact?
  • Are any wires frayed?

It's impossible to count how many seasoned mechanics have wasted an hour's diagnostics only to discover a ten cent blown fuse was the problem.

Circuit Checks

Most electrical system problems can be diagnosed by doing circuit checks and voltage tests. For this, you'll need an ohm meter or tester. Most DIY garages should have this as part of their standard tool set. Your next order of business will be to get detailed diagrams of your vehicle's electrical system - or at least the system in question. Most good automotive repair guides and engineering guides will have these included.

Test the circuits from all points, starting with load points. The load point is the item to be powered. Work your way back through the circuit(s) from there to the starting point (battery). Some paths are direct, some go through several relays and changes. Use your diagrams to follow.

Circuit tests are especially important if a fuse keeps blowing in use or an item's operation is intermittent. Often, a broken relay or faulty breaker can be found. Bypassing a circuit breaker can diagnose if it's the problem while relays are generally just replaced to test.

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