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CHECKING ELECTRICAL CIRCUITS

The electrical system of a car is a closed circuit with an independent power source 'the battery'

Apart from the main charging, starting and ignition circuits, there are other circuits that power lights, electric motors, the sensors and gauges of electrical instruments, heating elements, magnetically operated locks, the radio and so on
All Circuits are opened and closed either by switches or by relays - remote switches operated by electromagnets
Circuits have components connected to them,  and to operate these components they require voltage so, no voltage no function' which makes the first order of business when diagnosing electrical problems is to check the circuit's load point(bulb, wiper motor, any element the circuit is suppose to power) for the presence of voltage. If you find no voltage at the load point, you just uncovered the first clue about what a problem might be. Then you can check the fuse, fuse link, circuit breaker and also the relay supplying voltage to the circuit. A blown fuse should restore power once it's fixed and the cause of the fuse getting blown in the first case should be investigated

NOTE: Never replace old/blown fuse with a fuse of greater capacity. Even though the fuse may be able to handle a greater load, the rest of the circuit cannot

A bad relay or circuit breaker will have the same effect as a blown fuse, to easily check a circuit breaker bypass it with a jumper wire which has a replaceable inline fuse, this will protect the circuit from damage. If the circuit work, then the fault is from the circuit breaker

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