Wiring Harness (Short Circuit) - Test
A short circuit is a failure of an electrical circuit that results in undesired electrical current. Usually, a short circuit is a bypass of the circuit across a load. For example, a short across the wires in a lamp circuit produces too much current in the wires but no current is felt at the lamp. The lamp is shorted out. The resistance in a normal circuit can vary, but the resistance between a particular circuit and other unrelated circuits is always greater than 5 ohms. The following procedure explains the test for a short circuit.
Reference: For a complete electrical schematic, refer to the Electrical System Schematic for the machine that is being serviced.
TEST FOR A SHORT CIRCUIT
- Identify the connectors and the wire numbers of the suspect circuits. Use the Electrical System Schematic of the machine to identify the circuits.
- Turn the key start switch and the disconnect switch to the OFF position.
- Disconnect the component and the ECM from the wiring harness.
- At the machine harness connector for the ECM, place one of the multimeter probes on the contact of the suspect wire.
- Use the other multimeter probe to check the resistance across all other contacts in the connector(s) of the ECM and frame ground.
Expected Result: The resistance is greater than 5000 ohms for all the measurements.
OK - The resistance is greater than 5 ohms for all the measurements. The harness circuits are correct.
STOP.
NOT OK - The resistance is less than 5 ohms. There is a short in the machine harness. The short is between the suspected wire and the wire with the lowest resistance measurement.
Repair: Repair or replace the machine harness.
STOP.
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