Diagnosing electrical problems in your car can be tricky business. Maybe some lights go on and off, or the radio or clock has stopped working. Most of the time, our instinct to fix an electrical problem is to bang on the dash board a few times and hope whatever it is comes back on.
You may be lucky and just have a loose wire and banging just right on something might get it to fall back into place, but most times electrical problems are not that simple. Vehicles built in the 60s and 70s had very few electrically controlled devices as most things were controlled through a mechanical linkage. In the 80s and early 90s many automobile manufacturers started using vacuum controlled solenoids to operate small things like switches in the engine or the vents on your ventilation system. Since then, just about everything has become electronically controlled and regulated. Most of the electronics in your vehicle will last a very long time and never be changed, but when something does go wrong it can be difficult to pinpoint the problem.
If you are having a problem with an electrical component in your vehicle the first place to start is in the fuse box. Most cars have a few different fuse boxes. Most of the time, one is in the engine bay and a second is in the vehicle somewhere under the dash or on a kick panel. The engine bay fuse box usually holds the larger fuses for things like the alternator, electric fans or starter. The fuse panel inside usually houses the smaller fuses for things like the brake lights, clock and radio. There will be a diagram of which fuse goes to what on the underside of the cover or in your owner’s manual. Find the fuse for the component you are having problems with and pull it out. If the glass or plastic appears dark or burnt the fuses is probably blow and should be replaced.
If it turns out your fuse is good you can move on to checking the component itself. Make sure it is plugged in, free to move and not burnt or melted. Many of the electrical components on your vehicle can be tested without being removed by measuring a resistance value between certain contacts. If you’re handy with an ohm meter and have a repair manual for your vehicle you can test the component that way.
Another item to test if you are having electrical problems is the relay for that component. Relays are used in high power devices and are essentially electrically activated switches. When you turn your car on, multiple components turn on like the fuel pump, computer and electric fans. A small amount of power is run through the switch in your ignition which can then activate multiple relays turning all the peripheral equipment without running full power for all of them through the ignition switch. Relays also can go bad over time and cause electrical problems. The best way to test a relay is to have a helper touch or listen to the relay while you turn the device on. You should feel a slight tap and hear a quiet click as the relay engages.
If your problem is not with your electrical component, the fuse or the relay then you most likely have a wiring problem. Every electrical circuit needs to create a way for electricity to get to the device you are powering and also for the electricity to continue on back to the battery. If one of the wires delivering power or return power is not making a good connection, your electrical component will not work.
Bad connections can happen for a variety of reasons. As wires carry electricity they get hot, so it is possible after a lot of use for a connection to melt and no longer make contact. If the connect is outside of the cabin of the car it could get rusty or dirty to the point where electricity will no longer flow. It is also possible that from use and vibrations the wires simply disconnect. In this case you need a wiring diagram for your vehicle, a circuit tester and a lot of patience.
If you find yourself with a broken circuit make sure it is professionally repaired to make sure it doesn’t happen again. This may include replacing a single wire or an entire section of your vehicle’s wiring harness. Bad wiring can be difficult to track down and can cause a lot of problems with your vehicle. Make sure to have any electrical problems you have fixed quickly and professionally to avoid future problems and a possible fire hazard.
Pictures courtesy of:
Wiring – By Dave_7 in “1962 Volkswagen Beetle” Licensed by Creative Commons Share Alike 3.0 Via Flikr – Original Link
Fuse Box – By Mitch Barrle in “El Camino Restoration” Licensed by Creative Commons Share Alike 3.0 Via Flikr – Original Link