<ul><li>Prepare for ASE Electrical/Electronic Systems (A6) certification test content area “A” (General Electrical/Electronic Systems Diagnosis). </li></ul><ul><li>Explain the wire gauge number system. </li></ul><ul><li>Describe how fusible links and fuses protect circuits and wiring. </li></ul><ul><li>List the steps for performing a proper wire repair. </li></ul>OBJECTIVES: After studying Chapter 35, the reader should be able to:
<ul><li>adhesive-lined tubing • American wire gauge (AWG) • auto link </li></ul><ul><li>battery cables • blade fuse • braided ground straps </li></ul><ul><li>circuit breaker • circuit protection • cold solder joint • connector position assurance (CPA) • connectors • copper • crimp-and-seal connectors </li></ul><ul><li>fuse • fusible link cartridge • fusible links </li></ul><ul><li>heat shrink • jumper cables • lock tang </li></ul>KEY TERMS: Continued
AUTOMOTIVE WIRING <ul><li>Most automotive wire is made from strands of copper covered by insulating plastic. Copper is an excellent conductor of electricity that is reasonably priced and very flexible. Copper can break when moved repeatedly, so most copper wiring is constructed of multiple small strands that allow for repeated bending and moving without breaking. </li></ul>See this chart on Page 360 of your textbook. Copper is the best electrical conductor besides silver, which is far more expensive. Continued
<ul><li>American Wire Gauge All wire is sized and purchased to gauge size assigned by the American wire gauge ( AWG ) system. AWG numbers can be confusing because as the gauge number increases, the size of the conductor wire decreases . </li></ul>14-gauge wire is smaller than 10-gauge wire. The greater the amount of current (amps), the larger the conducting wire (smaller gauge number) required. Continued This chart that compares the AWG number to the actual wire diameter in inches. See this chart on Page 360 of your textbook.
<ul><li>Following are general applications for the most commonly used wire gauge sizes. </li></ul>NOTE: Always check the installation instructions or the manufacturer’s specifications for wire gauge size before replacing any automotive wiring. 20–22 gauge : radio speaker wires 18 gauge : small bulbs and short leads 16 gauge : taillights, gas gauge, turn signals, windshield wipers 14 gauge : horn, radio power lead, headlights, lighter, brake lights 12 gauge : headlight switch-to-fuse box, rear window defogger, power windows and locks 10 gauge : ammeter, generator, or alternator-to-battery Continued
<ul><li>Metric Wire Gauge Most manufacturers indicate on diagrams the wire sizes measured in square millimeters (mm 2 ) of cross-sectional area. This chart gives conversions or comparisons between metric and AWG gauge sizes. </li></ul>See this chart on Page 361 of your textbook. Notice the metric wire size increases with size (area), where the AWG gauge size gets smaller with larger-size wire. Continued
<ul><li>The AWG gauge number should be decreased (wire size increased) with increased lengths of wire, as shown here. </li></ul>See this chart on Page 361 of your textbook. Continued A trailer may require 14-gauge wire to light all the trailer lights, but if the wire required is over 25 feet long, 12-gauge wire should be used. Automotive wire, except spark plug wire, is often called primary wire as it is designed to operate at or near battery voltage.
Yes. The American wire gauge (AWG) sizing of wire includes all gauge numbers, even though the most commonly used sizes are even numbered, such as 12, 14, or 16. Because the sizes are so close, wire in every size is not commonly stocked, but it can be ordered for a higher price. Therefore, if a larger wire size is needed, it is common practice to select the next lower, even-numbered gauge. See the chart following for a comparison of the wire sizes. Do they make 13-Gauge Wire? See the complete AWG chart on Page 362 of your textbook.
<ul><li>AWG Gauge </li></ul>0000 000 00 0 1 2 3 4 5 6 7 8 9 10 11 12 13 0.46 0.4096 0.3648 0.3249 0.2893 0.2576 0.2294 0.2043 0.1819 0.162 0.1443 0.1285 0.1144 0.1019 0.0907 0.0808 0.072 Diameter (inches) This is a partial chart. See the complete AWG chart on Page 362 of your textbook. Do they make 13-Gauge Wire? YES!
BRAIDED GROUND STRAPS <ul><li>All vehicles use ground straps between the engine and body and/or between the body and the negative terminal of the battery. Many straps are braided and uninsulated, as seen in Figure 35–1. It is not necessary to insulate a ground strap because it does not matter if it touches metal since it already attaches to ground. Braided ground straps are more flexible than stranded wire, because the engine will move slightly on its mounts. Braided strap also dampens out some radio-frequency interference that might be transmitted through standard stranded wiring. The crossing of the wires in a braided ground strap effectively shorts out any AC voltage signal that contribute to radio interference. </li></ul>Continued
Figure 35–1 All lights and accessories ground to the body of the vehicle. Body ground wires such as this one are needed to conduct all of the current from these components back to the negative terminal of the battery. The body ground wire connects the body to the engine. Most battery negative cables attach to the engine.
The skin effect is the term used to describe how high-frequency AC electricity flows through a conductor. Direct current flows through a conductor, but alternating current tends to travel through the outside (skin) of the conductor. Because of the skin effect, most audio (speaker) cable is constructed of very small-diameter copper wires instead of fewer larger strands, because the smaller wire has a greater surface area and therefore results in less resistance to the flow of AC voltage. What is the Skin Effect? NOTE: Body ground wires are necessary to provide a circuit path for the lights and accessories that ground to the body and flow to the negative battery terminal. Continued
A twisted pair is used to transmit low-voltage signals using two wires that are twisted together. Electromagnetic interference can create a voltage in a wire, and twisting the two signal wires cancels out the induced voltage. A twisted pair means that the two wires have at least 9 twists (turns) per foot (13 twists per meter). What is a Twisted Pair?
BATTERY CABLES <ul><li>Battery cables are the largest wires used in the automotive electrical system. Usually 4-gauge, 2-gauge, or 1-gauge wires (19 mm 2 or larger). See Figure 35–2. Wires larger than 1-gauge are called 0-gauge (pronounced “ ought ”). Larger cables are labeled 2/0 or 00 (2 ought) and 3/0 or 000 (3 ought). Six-volt electrical systems require battery cables two sizes larger than those used for 12-volt electrical systems, because lower voltage used in antique vehicles resulted in twice the amount of current (amps) to supply the same electrical power. </li></ul>Continued
Figure 35–2 Battery cables are designed to carry heavy starter current and are therefore usually 4-gauge or larger wire. Note that this battery is covered with a thermal blanket covering to help protect the battery from high under-hood temperatures. The wiring is also covered with plastic conduit also called split-loom tubing.
JUMPER CABLES <ul><li>Jumper cables are 4- to 2/0-gauge electrical cables with large clamps attached, used to connect a vehicle that has a discharged battery to a vehicle that has a good battery. Good-quality jumper cables are necessary to prevent excessive voltage drops caused by resistance. Aluminum wire jumper cables should not be used, because even though aluminum is a good electrical conductor, it is less flexible and can crack and break. The size should be 4-gauge or larger. Ought-gauge welding cable can be used to construct an excellent set of jumper cables using welding clamps on both ends. Welding cable is usually constructed of many very fine strands of wire, which allows for easier bending. </li></ul>
FUSES AND CIRCUIT PROTECTION DEVICES <ul><li>Fuses should be used in every circuit to protect the wiring from overheating and damage caused by excessive current flow as a result of a short circuit or other malfunction. The symbol for a fuse is a wavy line between two points: • ~ • </li></ul><ul><li>A fuse is constructed of a fine tin conductor inside a glass, plastic, or ceramic housing. It designed to melt and open the circuit if excessive current flows through the fuse, according to its maximum current-carrying capacity. </li></ul>Continued
<ul><li>Many fuses are used to protect more than one circuit of the automobile. A typical example is the fuse for the cigarette lighter that also protects many other circuits such as those for the courtesy lights, clock, and other circuits. A fault in one of these circuits can cause this fuse to melt, which prevents operation of all other circuits that are protected by the fuse. </li></ul><ul><li>See Figure 35–3. </li></ul>NOTE: The SAE term for a cigarette lighter is cigar lighter because the diameter of the heating element is large enough for a cigar. The term cigarette lighter will be used in this book because it is common usage. Continued
Figure 35–3 This figure shows a typical automotive fuse panel.
<ul><li>Blade Fuses Colored blade - type fuses are referred to as ATO fuses. The plastic color of blade fuses indicates maximum current flow, measured in amp. Each fuse has an opening in the top to allow access to its metal contacts for testing purposes. The following chart lists the color and the amperage rating of blade fuses. </li></ul>Figure 35–4 Blade-type fuses can be tested through openings in the plastic at the top of the fuse. See the chart on Page 363 of your textbook.
<ul><li>Mini Fuses To save space, many vehicles use mini (small) blade fuses . They save space and allow the vehicle design engineer to fuse individual circuits instead of grouping many different components on one fuse. This improves customer satisfaction because if one component fails, it only affects that one circuit without stopping electrical power to several other circuits as well. </li></ul>Continued This also makes troubleshooting much easier, because each circuit is separate. See the chart on Page 363 of your textbook. The amperage rating and fuse color for mini fuses include:
<ul><li>Maxi Fuses A large version of blade fuses, called maxi fuses are used to replace fusible links in many vehicles. Maxi fuses are rated to 80 amperes or more. </li></ul>Continued See the chart on Page 364 of your textbook. The amperage rating and corresponding color for maxi fuses are shown here:
<ul><li>Pacific Fuse Element First used in the late 1980s, Pacific fuse elements (called a fuse link or auto link ) are used to protect wiring from a direct short-to-ground. The housing contains a short link of wire sized for the rated current load. The transparent top allows inspection of the link inside. </li></ul>Figure 35–6 A comparison of the various types of protective devices used in most vehicles. Continued
<ul><li>Testing Fuses It is important to test the condition of a fuse if the circuit being protected by the fuse does not operate. Most blown fuses can be detected quickly because the center conductor is melted. Fuses can also fail and open the circuit because of a poor connection in the fuse itself or in the fuse holder. Just because a fuse “looks OK” does not mean that it is OK. </li></ul>Continued
Figure 35–7 To test a fuse, use a test light to check for power at the power side of the fuse. The ignition switch and lights may have to be on before some fuses receive power. If the fuse is good, the test light should light on both sides (power side and load side) of the fuse. <ul><li>All fuses should be tested with a test light. The test light should be connected first to one side of the fuse and then the other. </li></ul>A test light should light on both sides. If the test light only lights on one side, the fuse is blown or open. If the test light does not light on either side of the fuse, then that circuit is not being supplied power. Use an ohmmeter to test fusible link cartridges .
<ul><li>Circuit Breakers Used to prevent harmful overload (excessive current flow). circuit breakers act by opening the circuit and stopping current flow to prevent overheating and possible fire caused by hot wires or electrical components. Circuit breakers are mechanical units made of two different metals (bimetallic) that deform when heated and open a set of contact points that work in the same manner as an “off” switch. See Figure 35–8. Cycling-type circuit breakers are reset when current stops flowing, causing the bimetallic strip to cool and the circuit to close again. A circuit breaker is used in circuits that could affect safety of passengers if a conventional non-resetting fuse were used. </li></ul>Continued
Figure 35–8 Typical blade circuit breaker fits into the same space as a blade fuse. If excessive current flows through the bimetallic strip, the strip bends and opens the contacts and stops current flow. When the circuit breaker cools, the contacts close again, completing the electrical circuit. Continued
<ul><li>The headlight circuit is an excellent example of the use of a circuit breaker rather than a fuse. Obviously, a sudden loss of headlights at night could have disastrous results. A circuit breaker opens and closes the circuit rapidly, protecting the circuit from overheating and also providing sufficient current flow to maintain at least partial headlight operation. Circuit breakers are also used in other circuits where conventional fuses cannot provide for the surges of high current commonly found in those circuits. Here are electrical symbols used to represent a circuit breaker: </li></ul>Figure 35–9 These electrical symbols are used to represent circuit breakers. Continued
<ul><li>PTC Circuit Protectors Positive temperature coefficient ( PTC ) circuit protectors are solid state (without moving parts). Like all other circuit protection devices, PTCs are installed in series in the circuit being protected. If excessive current flows, the temperature and resistance of the PTC increase. Unlike circuit breakers or fuses, PTC circuit protection devices do not open the circuit, but rather provide very high resistance between the protector and the component. See Figure 35–10. In other words, voltage will be available to the component. This has led to a lot of misunderstanding about how these circuit protection devices actually work. </li></ul>Continued
Figure 35–10 (a) Normal operation of a PTC circuit protector in a power window motor circuit. Note the many conducting paths. With normal current flow, the temperature of the PTC circuit protector remains normal. (b) When current exceeds the amperage rating of the PTC circuit protector, the polymer material that makes up the electronic circuit protector increases in resistance. As shown here, a high-resistance electrical path still exists even though the motor will stop operating as a result of the very low current flow through the very high resistance. The circuit protector will not reset or cool down until voltage is removed from the circuit. <ul><li>It is confusing when the circuit opens and the PTC circuit protector cools down. </li></ul>(a) (b) When the circuit is back on, the component may operate normally for a short time; however, the PTC resistance again increases to limit current flow. Continued
Figure 35–11 PTC circuit protectors are used extensively in the power distribution center of this Chrysler vehicle. Continued
<ul><li>Fusible Links A fusible link consists of a short length of standard copper-strand wire covered with a special nonflammable insulation. This wire is usually four wire numbers smaller than the wire of the circuits it protects. For example, a 12-gauge circuit is protected by a 16-gauge fusible link. </li></ul>Figure 35–12 Fusible links are usually located close to the battery and are usually attached to a junction block. Notice that they are only 6 to 9 inches long and feed more than one fuse from each fusible link. Special thick insulation over the wire may make it look larger than other wires of the same gauge number. Continued
<ul><li>If excessive current flow (caused by a short-to-ground or a defective component) occurs, the fusible link will melt in half and open the circuit to prevent a fire hazard. Some fusible links are identified with “fusible link” tags at the junction between the fusible link and the standard chassis wiring, which represent only the junction. Fusible links are the backup system for circuit protection. All current except the current used by the starter motor flows through fusible links and then through individual circuit fuses. It is possible that a fusible link will melt and not blow a fuse. Fusible links are installed as close to the battery as possible so they can protect the wiring and circuits coming directly from the battery. </li></ul>Continued
<ul><li>Checking Fusible Links Fusible links can melt and not show any external evidence of damage. To check a fusible link, gently pull on each end to see if it stretches. If the insulation stretches, the wire inside has melted and the fusible link must be replaced after determining what caused the link to fail. A nother way to check a fusible link is to use a test light or a voltmeter and check for available voltage at both ends of the fusible link. If voltage is available at only one end, then the link is electrically open and should be replaced. </li></ul>Continued
Corroded connections are a major cause of intermittent electrical problems and open circuits. The usual sequence of conditions is as follows: Look for the “Green Crud” <ul><li>Heat causes expansion. This heat can be from external sources such as connectors too close to the exhaust system. Another possible source of heat is a poor connection at the terminal, causing a voltage drop and heat due to the electrical resistance. </li></ul><ul><li>Condensation is created when a connector cools. The moisture in the condensation causes rust and corrosion. </li></ul>The solution is that if corroded connectors are noticed, the terminal should be cleaned and the condition of the electrical connection to the wire terminal end(s) confirmed. Many automobile manufacturers recommend using a dielectric silicone or lithium-based grease inside connectors to prevent moisture from getting into and attacking the connector.
TERMINALS AND CONNECTORS <ul><li>A terminal is a metal fastener attached to the end of a wire, which makes the electrical connection. The term connector usually refers to the plastic portion that snaps or connects together, thereby making the mechanical connection. Wire terminal ends usually snap into and are held by a connector. Male and female connectors can then be snapped together, thereby completing an electrical connection. Connectors exposed to the environment are also equipped with a weather-tight seal. See Figure 35–13. </li></ul>Continued
Figure 35–13 Some terminals have seals attached to help seal the electrical connections. Continued
<ul><li>Terminals are retained in connectors by the use of a lock tang . Removing a terminal from a connector includes the following steps: </li></ul>Figure 35–14 Separate a connector by opening the lock and pulling the two apart. Continued <ul><li>Release the connector position assurance (CPA) , if equipped, that keeps the latch of the connector from releasing accidentally. </li></ul><ul><li>Separate the male and female connector by opening the lock. </li></ul>Figure 35–15 The secondary locks help retain the terminals in the connector. <ul><li>Release the secondary lock, if equipped. </li></ul>
Figure 35–16 Use a small removal tool, sometimes called a pick, to release terminals from the connector. <ul><li>Using a pick, depress the lock tang and gently remove the terminal from the connector. </li></ul>
WIRE REPAIR <ul><li>Many manufacturers recommend that all wiring repairs be soldered. </li></ul>Continued Figure 35–17 Always use rosin-core solder for electrical or electronic soldering. Also, use small-diameter solder for small soldering irons. Use large-diameter solder only for large-diameter (large-gauge) wire and higher-wattage soldering irons (guns). Solder An alloy of tin and lead, solder makes a good electrical contact between two wires or connections in an electrical circuit. A flux must be used to help clean the area and to help make the solder flow. Solder made with resin (rosin) contained in the center, is called rosin-core solder .
<ul><li>Solder is available with various percentages of tin and lead in the alloy. Ratios are used to identify these various types of solder, with the first number denoting the percentage of tin in the alloy and the second number giving the percentage of lead. The most commonly used solder is 50/50, which means that 50% of the solder is tin and the other 50% is lead. The percentages of each alloy primarily determine the melting point of the solder. </li></ul><ul><li>60/40 solder ( 60 % tin/ 40 % lead) melts at 361° F (183°C). </li></ul><ul><li>50/50 solder ( 50 % tin/ 50 % lead) melts at 421° F (216°C). </li></ul><ul><li>40/60 solder ( 40 % tin/ 60 % lead) melts at 460° F (238°C). </li></ul>NOTE: The melting points stated here can vary depending on the purity of the metals used.
<ul><li>Because of the lower melting point, 60/40 solder is the most highly recommended solder to use, followed by 50/50. When soldering wires, be sure to heat the wires (not the solder) using a soldering gun or butane tool such as shown here. </li></ul>Figure 35–18 A butane soldering tool. The cap has a built-in striker to light a converter in the tip of the tool. This handy soldering tool produces the equivalent of 60 watts of heat. It operates for about 1/2 hour on one charge from a commonly available butane refill dispenser. Soldering a wiring splice includes the following steps: Continued <ul><li>While touching the soldering gun to the splice, apply solder to the junction of the gun and the wire. </li></ul>
<ul><li>The solder will start to flow. Do not move the soldering gun. </li></ul><ul><li>As the solder flows into and around the strands of the wire, keep feeding more solder into the splice. </li></ul><ul><li>A fter solder has flowed throughout the splice, remove the soldering gun from the splice; allow solder to cool slowly. </li></ul>The solder should have a shiny appearance. Dull-looking solder may be caused by not reaching a high enough temperature, which results in a cold solder joint . Reheating the splice and allowing it to cool often restores the shiny appearance. An acid-core solder is also available but should only be used for soldering sheet metal. Continued
<ul><li>Crimping Terminals Terminals can be crimped to create a good electrical connection if the proper type of crimping tool is used. Most manufacturers recommend a W - shaped crimp be used to force the strands of the wire into a tight space. </li></ul>Figure 35–19 Notice that to create a good crimp the open part of the terminal is placed in the jaws of the crimping tool toward the anvil or the W-shape part. Continued
Figure 35–20 All hand-crimped splices or terminals should be soldered to be assured of a good electrical connection. <ul><li>Most vehicle manufacturers also specify that all hand-crimped terminals or splices be soldered. </li></ul>
<ul><li>Heat Shrink Usually made from poly-vinyl chloride (PVC) or polyolefin, heat shrink tubing shrinks to about half of its original diameter when heated; called a 2:1 shrink ratio. Heat shrink by itself does not provide protection against corrosion, because the ends of the tubing are not sealed against moisture. Chrysler recommends all wire repairs that may be exposed to the elements be repaired and sealed using adhesive - lined heat shrink tubing. Usually made from flame-retardant flexible polyolefin with an internal layer of special thermoplastic adhesive. When heated, this tubing shrinks to one-third of its original diameter (3:1 shrink ratio), the adhesive melts, sealing the ends of the tubing. See Figure 35–21. </li></ul>Continued
Figure 35–21 A butane torch especially designed for use on heat shrink applies heat without an open flame, which could cause damage. Continued
<ul><li>Crimp-and-Seal Connectors General Motors Corporation and Ford Motor Company recommend the use of crimp - and - seal connectors as the method for wire repair. These are not simply butt connectors, they contain sealant and shrink tubing in one piece. </li></ul>Figure 35–22 A typical crimp-and-seal connector. This type of connector is first lightly crimped to retain the ends of the wires and then it is heated. The tubing shrinks around the wire splice and a thermoplastic glue melts on the inside to provide an effective weather-resistant seal. Continued
<ul><li>The usual procedure specified for making a wire repair using a crimp-and-seal connector is as follows: </li></ul>Figure 35–23 Heating the crimp-and-seal connector melts the glue and forms an effective seal against moisture. Step #1 Strip insulation from the ends of the wire (about 5/16 inch, or 8 mm). Step #2 Select proper size crimp-and-seal connector for the gauge of wire being repaired. Insert wires into the splice sleeve and crimp. Step #3 Apply heat to the connector until the sleeve shrinks down around the wire and a small amount of sealant is observed around the ends of the sleeve. Continued
<ul><li>Aluminum Wire Repair Many automobile manufacturers use plastic-coated solid aluminum wire for some body wiring. Because aluminum wire is brittle and can break as a result of vibration, it is only used where there is no possible movement of the wire, such as along the floor or sill area. This section of wire is stationary, and the wire changes back to copper at a junction terminal after the trunk or rear section of the vehicle, where movement of the wiring may be possible. </li></ul>Continued
<ul><li>Aluminum wire is protected in a plastic conduit, normally slit, after which the wires can easily be removed for repair. The following procedure should be used to be assured of a proper repair </li></ul>Step #1 Carefully strip only about 1/4 inch (6 millimeters) of insulation from the aluminum wire, being careful not to nick or damage the aluminum wire case. Step #2 Use a crimp connector to join two wires together. Do not solder an aluminum wire repair. Solder will not readily adhere to aluminum because the heat causes an oxide coating on the surface of the aluminum. Step #3 To prevent corrosion, the spliced, crimped connection must be coated with petroleum jelly. Step #4 The coated connection should be covered with shrinkable plastic tubing or wrapped with electrical tape to seal out moisture.
Most electrical wiring is protected with a plastic convoluted conduit, which comes in many different grades depending on the temperature of the surrounding area. A painted stripe usually indicates that the conduit is designed for high-temperature applications and is used where it would be placed on or near the engine. Do not use inexpensive conduit around wiring that will be exposed to temperatures higher than 200°F (85°C). What Does the Stripe on the Plastic Conduit Mean? Figure 35–24 The color stripe on the side of the convoluted conduit indicates that the conduit is designed for high-temperature applications.
SUMMARY <ul><li>The higher the AWG size number, the smaller the wire. </li></ul><ul><li>Metric wire is sized in square millimeters (mm 2 ) and the higher the number, the larger the wire. </li></ul><ul><li>All circuits should be protected by a fuse. The current in the circuit should be about 80% of the fuse rating. </li></ul><ul><li>Circuit breakers and fusible links are other circuit protection devices. </li></ul>Continued
SUMMARY <ul><li>A terminal is the metal end of a wire, whereas a connector is the plastic housing for the terminal. </li></ul><ul><li>All wire repair should use either soldering or a crimp-and-seal connector. </li></ul>( cont. )