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Lights, Fuses and Flashers, Page 2 of 2

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Fuses, fusible links and circuit breakers

All wires must be insulated and protected from overload. If the insulation breaks (creating a path for electricity that was not intended) or if the circuit is overloaded, the fuse, circuit breaker or fusible link that protects the circuit will "blow."

Fuses
See Figures 15, 16, 17, 18 and 19

Fuses never blow because of high voltage. High amperage in the circuit, greater than the capacity of the fuse, causes the metal strip to heat up, melt and open the circuit, preventing the flow of electricity. A fuse could carry 200 volts as well as 2 volts, but will only tolerate its rated amperage and about 10% to handle minor current surges before it blows.

Auto fuses come in several designs, but all usually consist of a zinc strip or a piece of wire. Heavier load fuses have a notch in the middle of the zinc strip. The wider section at each end is to give better temperature-carrying capability. The heat from a temporary overload is transferred to the wider metal and slows fuse burnout. In case of a heavy overload, the metal strip will melt in a fraction of a second and protect the circuit.

The old glass fuse, used in older model cars is primarily used in accessory applications today. On all late model cars, you'll likely find a fuse that is different from the old glass tube fuse. It's a miniaturized, blade-type design that is referred to as ATC, ATM, or MAX fuse. The "blade-type" was developed in conjunction with the smaller fuse block. Fuses of different ratings are interchangeable but amperage ratings are molded in color-coded numbers that match the fuse ratings on the fuse block. The following chart identifies the amperage and color code.

Normally the fuse box is somewhere under the dash or in the engine compartment. Burned out fuses are readily identified by the burned zinc element in the middle of the glass, plastic, or ceramic insulator. Small, inexpensive plastic tools are available to easily replace a burned fuse. Never replace a fuse with one of a higher load capacity (the amperage is usually stated on the fuse).

Figure 15 Blade-type fuses - color code denotes amperage.
  ATC ATM MAX
Black 1    
Gray 2 2  
Violet 3 3  
Pink 4 4  
Tan 5 5  
Brown 71/2 71/2  
Red 10 10 50
Lt. Blue 15 15 60
Yellow 20 20 20
Clear 25 25  
Green 30 30 30
Amber 40   70
Orange     40
Natural     80

Figure 16  Old glass-style fuses are used primarily for accessory applications in today's late-model cars.
Old Style Glass Fuses

Most people's reaction when a fuse blows is simply to replace it and see if the problem reoccurs. Well, if the new fuse blows too, then there is something wrong with that circuit -- meaning you should figure out the problem and fix it rather than just continuing to replace fuses. Check the wiring to the components that are run off the blown fuse, look for bad connections, cuts, breaks or shorts which would allow the circuit to complete without the proper load or which would add such a large additional load that the fuse would blow. Sometimes just wiggling the harness will be enough to stop the problem (remove a short or make a better connection), BUT, unless you find the broken wire or fasten the loose connector, the fuse will likely blow again later.

Figure 17  A blade type fuse is bad if there is a break in the element.
A blade type fuse is bad if there is a break in the element.

Figure 18  A hairline break is hard to see, but represents a bad fuse, too.
A hairline break is hard to see, but represents a bad fuse too.

Figure 19  To use a puller, simply grasp the fuse, then pull it out.
To use a puller, simply grasp the fuse, then pull it out.

Circuit breakers
See Figure 20

Circuit breakers are sealed assemblies that perform the same job as the fuse, but in case of an overload, will cut current for an instant. Unlike a fuse, things will return to normal. They rarely go bad but must be replaced with an identical unit should one blow. As with fuses, if a circuit breaker continues to fail, the source of the trouble should be found and corrected.

The main advantage of a circuit breaker over a fuse is what happens when the circuit breaker does its job. When a fuse blows, it becomes trash, while the circuit breaker can cool and reset (to be used over and over again). For this reason, circuit breakers tend to be used to protect high load circuits, on which an occasional overload is expected. Accessories such as power windows or seats which use powerful motors (which might occasionally draw too high an amperage if they encounter mechanical resistance) are good candidates for circuit breaker protection.

You never know exactly where to look for a circuit breaker, but many times, they are located near the fuse box or near the component they protect. On some cars, the circuit breaker that protects the headlights is an integral part of the headlight switch, which must be replaced in its entirety.

Circuit breakers are designed to offer a variety of performance characteristics including three types of reset.

Always follow the OEM's recommendations when replacing circuit breakers. Replace only with the same type breaker in aftermarket applications.

  • Type I -- Automatic reset. Circuit breaker automatically resets after opening, if the fault still exists, the breaker will continue to cycle between ON and OFF positions until the overload is corrected. These devices are sometimes called "cycling breakers."
  • Type II -- Modified reset. The circuit breaker will remain tripped (in the OFF position) as long as there's power to the circuit due to an internal resistor. Type II breakers can be reset by turning off the circuit, or by turning off the ignition switch. These devices are sometimes called "non-cycling breakers."
  • Type III -- -Manual reset. The circuit breaker will remain tripped (in the OFF position) until an indicator button or lever is manually reset.

Figure 20 Circuit breakers come in a variety of styles and sizes, and can be mounted almost anywhere. They may be mounted in the line they protect, or plugged into the circuit at the fuse box.
Circuit breakers come in a variety of styles and sizes.

Fusible links and maxi fuses
See Figures 21, 22 and 23

Fusible links are a piece of wire about 6" long which is spliced into another wire, usually a gauge or two smaller than the wire it protects. Fusible links can be found almost anywhere. Many times they are identified by a colored flag on the link, or by a loop to make it stand out from other wires, and are usually the same color as the protected circuit. Some fusible links may burn in half with no change in appearance, but most are covered with a special insulation that will bubble and char when the fusible link burns.

Fusible links should always be replaced with an original-equipment type.

Figure 21  Most fusible links show a melted, charred insulation when they burn out.
Most fusible links show a melted, charred insulation when they burn out.

On most modern cars the fusible link has been replaced by the maxi fuse. The maxi fuse is a much larger version of the common standard size fuse (designed to carry the large loads of fusible links) and which have the advantage of being replaced much more easily than the old style fusible link.

Figure 22  Mini, standard and maxi fuses are used in most newer cars.
Mini, standard and maxi fuses are used in most newer cars.

Figure 23  A maxi fuse can be pulled out of the block in the same manner as a standard fuse.
A maxi fuse can be pulled out of the block in the same manner as a standard fuse.

Flashers
See Figure 24

The flasher consists of a blade and resistance ribbon, which holds the blade in a bent position, until the flasher-circuit is activated. Current flows through the ribbon, heating it so that it elongates and relaxes its tension on the blade. The blade snaps away from the ribbon, breaking the circuit. In the absence of current, the ribbon cools rapidly and shrinks in length until the blade is pulled back into contact with the ribbon. This heating and cooling cycle causes the flashing action in the circuit. Essentially, the flasher is a timed relay, the timing of which is dependent upon the current in the circuit and the mechanical design of the flasher itself.

Flashers are found in all sorts of out-of-the-way places. They are usually small metal or plastic (round or square) units that plug into the fuse box, and they operate the turn signal indicators and the hazard warning system. These don't go bad very often, but suspect the flasher if all the bulbs are in good condition. Conversely, check the bulbs first, because the flashers are designed to stop working if one of the bulbs burns out alerting the driver to a potential problem.

If you can't find the flasher right away, turn on the ignition and the turn signals and start hunting for the noise. When you find it, you'll be able to feel the vibration in the relay. Most flashers plug in and can usually be replaced by feel, even if you can't see them.

Figure 24  The flasher or fuse block can be found almost anywhere, depending on the year and model of the car.
The flasher or fuse block can be found almost anywhere depending on the year and model of the car.


Periodic maintenance for lights, fuses and flashers

Maintenance locations for lights, fuses and flashers
Lights, fuses and flashers give little warning before they go bad. About the only thing you can do is to periodically check the bulbs to be sure they are working. Fuses and flashers will give immediate evidence that they have ceased functioning.

Check operation of bulbs Every 1,000 miles/1 month

See troubleshooting basic lighting problems

See troubleshooting basic turn signal and flasher problems

 

 

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1998 W. G. Nichols - Chilton's Easy Car Care