How to Test a Circuit Breaker in a Car

by Steve Smith
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When things do not work on your car like the stereo, headlights, or dome light the first thing you should test is the circuit breakers. This saves a lot of time and money. Replacing a simple 15 cent circuit takes only 10 minutes, but replacing a stereo you believe to be dead will take at least two hours and cost at least $100. Using a volt meter and basic car knowledge you will be able to test all your circuit breakers with relative ease.

Step 1

Turn the car off, if it is on, and then locate the car's fuse box. The fuse box is typically mounted under the dashboard on the driver's side, or near the glove box on the passenger side.

Step 2

Gain access to the fuse box and remove whatever is in the way (if necessary) with a screwdriver. This might include interior paneling and dashboard trim.

Step 3

Remove the circuit you intend to test with your fingers. Turn on the car. Touch one of the voltmeter's metal prongs to the positive connector called the "hot" connector, on one side of the circuit board, and the other metal prong to the "cold" or negative terminal in the circuit board.

Step 4

Read the resulting voltage which displays on digital voltmeters in numeral form, or through a needle dial gauge reading in traditional voltmeters. Repeat the test as necessary to confirm your readings. If there is no voltage, it means the circuit is dead and there is a problem with the board or the wiring to the board. Turn the car on and off again, and retest the circuit to confirm this reading.

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