There are two signs of a connection failure. The first one is the obvious one: total failure. This can manifest itself in the stereo unit not turning on, or the stereo being on but not producing any sound from the speaker. When it is a problem with a speaker connection, it will usually only be one speaker that has the problem. The others may still have good contact while that one is failing.The second type of failure is poor connections. This will cause a reduction in system performance (such as volume), static, or the sound intermittently cutting out. These problems can be harder to troubleshoot than full failure.Many of these problems occur because of poor connections on the part of the installer. Good electrical connections are both mechanically and electrically sound. "Mechanically sound" refers to the physical connection being sufficiently firm so that it does not come loose easily. "Electrically sound" refers to the ability for the connection to pass electrical current without being interrupted or attenuated (reduced in strength). It is impossible for an electrical connection to be electrically sound if it is not mechanically sound. However, it is common to have connections that appear to be mechanically sound but are not electrically sound.The absolute best electrical connection for avoiding connection failure is a soldered one. A proper solder job provides a connection that is both mechanically and electrically sound, and that cannot be affected by vibration or corrosion. After soldering, the next best connection is a crimp connection. While these maintain mechanical integrity, they can corrode, reducing electrical connectivity. Electrical connections should never be made by simply twisting wires together, as there is no guarantee of maintaining electrical connectivity.Tools Needed for Electrical TroubleshootingIn addition to a screwdriver or two, which will be useful for getting into enclosures and behind panels in the car, there are a few basic tools that make troubleshooting much easier:A multimeterA flashlightTwo wires with alligator clips on both endsA 9- volt batteryWith these few tools, you can troubleshoot any connection problem in a car stereo system.How a Multimeter WorksBefore getting into actual troubleshooting, it is necessary to understand the basics of how a multimeter works. These devices are designed to measure three things: DC voltage (direct current), AC voltage (alternating current), and impedance. All three of these measurements can be useful in in troubleshooting audio systems. Most multimeters have a rotary dial for selecting the meter’s range. The AC and DC voltage settings will probably be shown by those abbreviations ("AC" and "DC"), and impedance will usually be shown by the Greek letter "?" (Omega). Within each of these areas of the meter, there will be several settings that show the maximum amount of voltage or impedance measured.Multimeters come supplied with two leads, a red one and a black one. The red one is used for positive and the black one for "common" or "ground." These are mostly important when measuring DC voltage. If the meter has three connections for the leads, one will be used for measuring amperage. It will be identified by "+10A" or something similar. Do not use this connection.Analog multimeters will show a reading immediately upon connection. On the other hand, digital meters need a few seconds to register a reading.Tip 1 - Some Basics About TroubleshootingTroubleshooting is a logical process of eliminating possibilities. In the case of troubleshooting a car stereo system, what needs to be eliminated is the bad connection or component. For audio systems, it is best to start from the source of the signal and work toward the speakers. In other words, start from the receiver, and then check theamplifier, the signal processor, and the speakers. Remember that the problem is more likely to be caused by a connection than a component.The first step in any troubleshooting endeavor is to look at the symptoms of the problem, to determine what is not working and what is. If something is working properly, then the problem is not with that component, and it can be ruled out. In most cases, all components, other than the speakers, will have a power LED light to indicate that the component has power. If these are not lit, then the problem is a power problem.Tip 2 - Troubleshooting Power ProblemsIf the visual inspection shows that the power on LED is not lit for a particular system component, then there is a power problem with that component. First, check that the power switch is on and has not been bumped off inadvertently. The next step is to check the fuse for that component, which could be mounted in the panel of the unit, near the power cord entry, or could be inline.Most fuses can be checked by visual inspection. If the filament is visible and intact (no broken spots), then the fuse is good. If the filament is not visible, or a section of it is missing, then the fuse is bad. If it is impossible to check the fuse visually, a multimeter can be used. Set the meter to check impedance (?) and touch one lead to each of the contacts on the fuse; the impedance should be about 0 ohms.If the fuse is good, the next step is to verify that there is power at the connection where the power leads are attached. If the power leads for the device are on a connector, this can be best checked at the connector. Set the multimeter to check for 20 VDC (volts direct current). Disconnect the power connector and attach the red lead to the power pin in the connector (it will probably be a red wire) and the black lead to the negative pin of the connector (it will probably be a black wire). The reading should be 12 VDC to 14.5 VDC.If there is no power connector, check the power wherever the leads connect to the vehicle. The red power lead should be connected to the fuse box or the battery
, and the black one should be connected to ground. Ground on any car is the vehicle’s metal chassis and body.Please note that it is possible to connect the negative lead to metal and still not have a good ground. Modern cars use much more plastic than older ones did. Therefore, it is possible to have a metal bracket that looks like a good ground, but is not connected to any other metal. Also, paint on a metal part can prevent a good ground. When in doubt, temporarily run a wire to the negative terminal of the vehicle’s battery to check.Visually check that the connections are not corroded. Corrosion will appear as a discoloration of the metal. Light corrosion can be cleaned off with a pencil eraser; heavy corrosion must be cleaned off with a wire brush.Tip 3 - Troubleshooting Signal ProblemsThe sound signal leaves the stereo system and goes either directly to the speakers or to an amplifier. If it is going to an amplifier, it is possible that the signal is not reaching the amplifier due to a bad connection or a broken wire.Start by checking the wires. There are three things that can go wrong with a wire: corrosion, a short circuit, or a broken wire. Disconnect the wires at both ends and visually check them for corrosion. Any corrosion will appear as a discoloration to the connector. It can be cleaned off with a pencil eraser.Reconnect and disconnect the connection again. It should require some force to connect and disconnect the connectors. If the connectors are overly easy to connect and disconnect, it is possible that a good mechanical connection is not being made. If this is the case, carefully adjusting the pins to tighten them can solve the problem.With the cable disconnected at both ends, check for a short circuit by connecting the multimeter, set for ohms (?), to the two terminals. If it does not show a reading, this means that there is infinite impedance. Short the terminals at one end of the cable together with the wire and alligator clips. The impedance should now read 0 ohms.If the multimeter reads 0 ohms before connecting the wire and alligator clips, then there is a short circuit in the wire. If it reads 0 ohms with the alligator clip short, then the wire is broken. Visually inspect the wire throughout its length to find any place where the wire is pinched. That is probably where the problem is coming from.Tip 4 - Troubleshooting Speaker ProblemsTroubleshooting speaker problems is similar to troubleshooting signal problems. The speaker wire pairs can be checked with the multimeter for shorts and broken wires in the same way as the signal wires. In addition, there is a much easier way to check the wires. Disconnect the speaker wires from the amplifier. Connect the wires with the alligator clips on them to the terminals of the speaker wire connector, taking care to ensure that they are not touching each other. Brush the clips at the other end of the wire across the two terminals of the 9-volt battery, again taking care to ensure that they are not touching each other. A static sound should come out of the speaker.If no sound comes out of the speaker, the speaker itself can be checked with the multimeter. Disconnect the wires from the speaker, and set the multimeter to measure a 20-ohms range. Connect the two leads of the multimeter to the two terminals on the speaker. It should read 2, 4, or 8 ohms, depending on the type of speaker. If it reads either 0 ohms or infinite ohms (nothing), this means the speaker itself is bad.A bad speaker usually indicates that the voice coil is shorted or burnt out. Speakers can be repaired. Since the voice coil is attached to the back of the cone, they are replaced together.