# Circuit Failures

Open Circuit

Click on the bulb mark or the underlined sentence.
An electrical device operates normally if there are no malfunctions in its circuit. The voltage at the connectors can be measured as shown in the diagram.
However, if an electrical device does not operate normally, its circuit may have failed in some manner.
In this case, the area of a malfunction can be identified by measuring the connectors.

Identifying the area of a malfunction
Suppose a light bulb does not illuminate (or an electrical device does not operate normally) as shown in the diagram.
By measuring the voltage in each area, it becomes evident that there is no voltage after connector A (or C).
This indicates that the conductor is disrupted at connector A (or C), which stops the flow of the current.
This type of failure is called an open circuit.

Poor Circuit
If there are no problems in the circuit, the light bulb in the circuit will illuminate brightly.
However, if the light bulb illuminates dimly, there may be a malfunction in this circuit.

Identifying the area of a malfunction
A voltage check at each end of the light bulb in the circuit has detected
9 V.
In this circuit, the normal voltage at each end of the light bulb is 12 V.
Because this is a direct current circuit, this symptom indicates the presence of a resistor other than the light bulb.
A subsequent voltage check at each end of the switch has detected 3 V.
This indicates that the switch presents resistance, possibly due to a poor contact.

Short Circuit
Supposing that the fuse has blown in the circuit, check the cause of the blown fuse.
Identifying the area of a malfunction
The function of a fuse is to prevent wiring or equipment from being damaged by opening the circuit as a result of heating and melting when excessive amperage flows through it.
For this reason, it can be assumed that excessive amperage has flowed through this circuit.
Because this is a direct current circuit in which the voltage remains constant, there is the possibility of a short circuit between the wiring harness and ground that caused the excessive amperage to flow.
Upon measuring the resistance between each connector and ground, 0 Ω has been detected at connector B.
This indicates that connector B has shorted to ground, causing an excessive amperage to flow through this circuit.