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    Fuse

    Inspect/Test/Replace

    A fuse failure could be a once only occurrence or there could be an electrical problem that must be fixed. Replacing a fuse or fuse link or resetting a circuit breaker does not fix the problem that caused the overload. The overload device will probably just fail again. Always fix the problem before restoring circuit protection.

    Automotive fuses are rated according to current capacity, not voltage. A 12-volt fuse will also work in a 110-volt application. Voltage does not cause a fuse to blow, current does. Fuses have a ten percent overload factor to guard against minor power surges.

    To find a ground:

    • Locating the cause of a grounded circuit with a test light is not usually possible because the fuse blows as soon as the circuit is energized.
    • A circuit breaker can be installed temporarily in place of a fuse for diagnosing grounded wires.
    • Install a test light in series with the circuit breaker while making the test.
    A test light installed with a circuit breaker for finding a faulyt circuit.
    • Disconnect individual circuits until the light goes out.
    • The circuit that was disconnected when the light went out is the one at fault.
    • A compass or Gauss meter or gauge ( a gauge that detects magnetism) can be used to located that exact location of a ground when a wire has been accidentally pinched.
    Use a compass or Gauss gauge to check for changes in the magnetism in the circuit at the location of the pinched wire.
    • Another method of detecting a grounded circuit is to use an ohmmeter. Connect it to the circuit side of the fuse holder and ground.
    NOTE
    Be careful not to allow the ohmmeter to contact the power side of the fuse holder. When there is continuity between the load and ground, the circuit is grounded.

    To test a fuse:

    • The fuse panel is usually under the hood, under the instrument panel, or in a kick panel in the driver's compartment. With the fuse in the socket, a test light can be used to test the fuse.
    • With one end of the test light clipped to the ground, the tester should light up when probing both sides of the fuse.
    • If the tester glows only when touched to one end of the fuse, the fuse is defective. (The side that does not light is the ground side of the circuit.)
    • The end of a blade-type fuse has a small hose that exposes its fuse metal to the outside of the fuse so it can be probed with a test light.
    NOTE
    If you use a screwdriver or needle nose pliers to remove a glass cartridge or ceramic fuse wear eye protection. The glass tube or the ceramic body could shatter.

    To test the fuse socket:

    • With the fuse removed, use the test light to determine which side of the fuse socket is the ground side.
    • The tester will not light when attached to that side.
    • If the tester does not glow on either side of the circuit:
      • The circuit is shut off.
      • The circuit is broken.
      • The tester does not have a good ground connection.

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