Power Centers are all about power. Not horsepower but routing electrical power through the various circuits and accessories in the vehicle's electrical system. Think of the Power Center as a fuse box on steroids. And because it is the heart of the entire electrical system, you can use it as a handy access point for checking circuit voltages, resistance and continuity. Compared to the random locations of fuses and relays throughout the electrical system in older vehicles (those built up until the mid- to late-1980s), the Power Center is a welcome improvement. With most of the relays and fuses grouped together inside one or two plastic boxes, and labeled so you can identify the fuses and relays inside, the Power Center provides a great place to start your electrical diagnosis. Many vehicles may also have one or more separate fuse panels inside the vehicle (usually under the instrument panel or under a side kick panel) that hold fuses for lower amperage electrical accessories and circuits such as radio, power seats, windows, power outlets, horn, interior lights, etc. But most of the high amperage circuits are routed through the power center rather than a smaller interior fuse panel. The power center is located in the engine compartment. It is usually a large rectangular plastic box with a removable cover. If you can't find it, refer to your vehicle owners manual for its location. When you open the cover on the power center, you will see various fuses and relays that protect and control the electrical circuits in your vehicle. The fuses and relays are usually identified on the inside of the power center cover. If not, you will have to refer to your owners manual or the vehicle service literature to figure out which fuses and relays are associated with which electrical circuits in your vehicle. This is what you'll find inside the power center when you open the lid. The fuses and relays are often identified inside the power center cover. If you are replacing a blown fuse, replace it with a fuse that has the SAME amp rating as the original. NEVER substitute a fuse with a higher amp rating as this can increase the risk of circuit damage or an electrical fire! WHAT FUSES DO Fuses are circuit protection devices. A fuse prevents electrical overloads in a circuit that can overheat and melt wiring, possibly causing a fire or damage to the wiring or other electrical or electronic components. Each fuse has a specific amp (current) rating. When the current in a fused circuit exceeds the amp rating of the fuse, the heat-sensitive wire or blade inside the fuse melts. This "blows" the fuse, opens the circuit and stops the flow of electricity to protect the wiring and other devices connected to that circuit. Up until the 1980s, most vehicles used snap-in style fuses with a short piece of wire inside a hollow glass tube. In newer vehicles (1990s and up), blade-style transparent plastic fuses are used (both "mini" and "maxi" sizes). Mini-fuses are typically used for circuits that normally handle no more than 20 to 30 amps. Maxi-fuses are typically used for circuits that carry higher amp loads (40 up to 120 amps). The number on the fuse is its maximum amp rating. Most fuses are the push-in spade type, but some larger capacity fuses may be bolt-in. A blown fuse can be identified by visually inspecting the fuse. This may require removing the fuse from its holder. If the wire inside the fuse is broken, the fuse has failed and must be replaced with one that has the exact same amperage rating as the original. Replacing a Blown Fuse If a fuse has failed, the device or circuit that the fuse protects will not work until the fuse is replaced. IMPORTANT: Make sure the ignition is OFF and the circuit/device that has the blown fuse is OFF before replacing a fuse. With spade style standard and mini fuses, the fuse simply pulls out of its socket. You can use your fingers, a plastic fuse puller tool or small pliers to remove the blown fuse. For bolt-in maxi fuses, you will need a nut driver or screw driver depending on how the fuse is attached inside the power center or fuse panel. A plastic fuse puller tool makes it easy to extract a blown fuse from a fuse panel. Use the tool to grasp the top of the fuse, then pull outward to remove the fuse. The replacement fuse can now be pushed or bolted into place to restore power to the circuit. Warning: Never substitute a fuse with a higher amp rating as doing so may result in circuit damage or a fire! Also, never remove or install a fuse when a circuit is on. Fuse amp ratings are marked on the fuse so you can choose the correct replacement fuse. Also, fuses are color coded so make sure the replacement fuse is the same color as the original. After the new fuse has been installed, turn the ignition on or start the engine, then turn on the device that had the blown fuse to see if the circuit is now working normally. If the new fuse immediately blows or the device is still not working, there is likely a short circuit that will have to be found and repaired. For help with this kind of problem, see Troubleshooting electrical problems. High amperage fuses of the type found inside a power center. Other Types of Circuit Protection A "fusible link" is another type of circuit protection device that functions the same as a fuse (it melts when the load exceeds the rated current). The only difference is that a fusible link is a length of special wire that is permanently wired into a circuit or wiring harness. If it fails, the section must be cut out so a new fusible link can be spliced in. You can usually spot a failed fusible link by looking for blistered insulation around a wire. In most newer vehicles, high power fuses have replaced fusible links. This makes both access and repair much easier. A "circuit breaker" is another type of circuit protection device that may be used in electrical circuits (such as the headlights or wipers) that may experience occasional overloads. Think of a circuit breaker as a fuse that can reset itself. Instead of a wire that melts if it gets too hot, a circuit breaker uses a heat-sensitive bimetal contact arm and contact points to open a circuit if it overloads. After the circuit breaker cools down, the contacts re-close and current is restored. There are also circuit breakers that must be manually reset by pressing a pin or button on the unit. WHAT AUTOMOTIVE ELECTRICAL RELAYS DO A relay is a switching device that uses a small electrical current to control a much larger current in a second circuit. In other words, a relay routes power to a circuit or component when it is turned on. Relays are typically used for components that draw a large current such as the headlights, rear window defogger, fuel pump, A/C compressor clutch, cooling fan(s), heater & A/C blower fan, ABS system, the ignition circuit, even the power windows, seats and horn. A relay is nothing more than a small rectangular box (usually plastic but may also be metal) with a magnetic coil, armature and set of contact points inside. There are typically four or five spade terminals on the bottom of the relay, and the cover may or may not have a simple wiring schematic or other identification printed on it. When voltage is applied to the coil inside the relay, the coil creates a strong magnetic field and pulls the armature down to close the contact points. This allows voltage to pass through the output side of the relay to the device it controls. There are three basic types of relays: * Normally open are the most common type. The armature closes when the coil is energized to route power to a circuit or component. * Normally closed. The armature is normally closed and is pulled open when the relay is energized to turn OFF a circuit or component. * Dual relay. This type of relay routes power one way when it's off and another way when it is on. Many vehicles use more than one type of relay in a particular circuit (such as the A/C compressor clutch circuit), and may use the same relay to control more than one device. ELECTRICAL RELAY FAILURE Relays that carry high loads and are constantly switching on and off have higher failure rates than relays which are seldom used or only carry low amp loads. If a relay fails, it will prevent power from reaching the device it controls. In the case of a fuel pump relay, a failed relay will prevent the engine from starting because there will be no fuel pressure. If a cooling fan relay fails, the engine may overheat because the electric cooling fan never comes on. If an A/C compressor clutch relay fails, the compressor won't engage and there will be no cold air from the A/C. On most Chrysler vehicles, for example, the cooling fan relay must be engaged before power can go to the A/C compressor clutch. If the fan relay has failed, it will prevent both the fan and the compressor clutch from operating. RELAY ELECTRICAL DIAGNOSIS If an electrical component isn't working, the first thing that should always be checked is the wiring circuit that provides power to the component. Start with the fuse(s). If a fuse has blown, chances are the problem isn't just the fuse but a short or electrical overload in the circuit or device it protects. Replacing the fuse may only fix the problem temporarily — and if the new fuse blows immediately, it means there is a serious electrical problem that will require further diagnosis. If all the fuses are intact and there is no power to a component, the relay(s) for that component should be the next item checked. In many instances, a suspicious relay can be bypassed with a fused jumper wire to see if rerouting power restores proper operation of the device (as when bypassing the fuel pump relay to see if the fuel pump will run). If bypassing the relay restores normal operation, the relay is at fault and must be replaced. If bypassing the relay changes nothing, further diagnosis of the power supply and ground circuits as well as the wiring harness and circuit components will b…

Fonte: AA1Car.com