RELAY 3074517 - Caterpillar

Circuit Faults
The following information will describe the circuit malfunctions of series, parallel, and series parallel circuits.Circuit Malfunctions
There are several ways that a circuit can malfunction. Most electrical malfunctions are caused by the following conditions: opens, shorts, grounds, high resistance, or intermittents.Opens
An open in any part of a circuit is an extremely high resistance that results in no current flow in the circuit. An open can be caused by any of the following components that have failed:
Switch
Fuse
Broken wire
Connector
Component (load)The physical location of the open determines how the circuit will react. In a series circuit, any open connection will result in no current flow in the circuit. Illustration 1 shows an open in a series circuit. The switch acts as an open. Therefore, no current will flow through the two loads when the switch is open.
Illustration 1 g01070634
Troubleshooting an open circuit is easily accomplished by using a multimeter and by measuring the source voltage. If source voltage is available at the connection ahead of the switch and not available on the load side of the switch, the switch contacts are open. If voltage is available on the load side it would be necessary to continue checking the circuit until the open is identified.In a parallel circuit, identifying an open depends on where the open occurs. If the open occurs in the main line, none of the loads or components will work. All parallel branches will not operate. Additionally, an open in the return ground path would have the same effect as an open in the main line. An open in the return ground path is referred to as an open ground.If the open occurs in any of the branches below the main line, only the load on that specific branch is affected. All other branch loads will operate normally. Illustration 2 shows an example of an open in the main line and in a parallel branch.
Illustration 2 g01070636
When you are troubleshooting or diagnosing an open in a circuit, the result is normally a component that fails to operate or to function. Since most circuits are protected with some type of a fuse or circuit protection device, it is recommended that the fuse or device be checked visually. If a visual check does not reveal an open condition, remove the device and perform a continuity check in order to ensure that the device is functional. The next most probable place to check for an open is at the component. Using a multimeter and a electrical schematic, determine if the system voltage or source voltage is available. If voltage is not present at the component, the next step is to determine what other electrical devices, such as switches or connectors, are in the circuit path. Eliminate those devices, starting at the easiest location and working back toward the voltage source.Shorts
A short in a circuit is a direct electrical connection between two points. There is usually a very low resistance or opposition to current flow. A short in a circuit often describes an unwanted or