770G and 772G Off-Highway Truck/Tractors Caterpillar

An open circuit is a failure of an electrical circuit that results in no flow of electrical current. An open circuit can be caused by a broken wire within the circuit. Most often, an open circuit is caused by a poor connection. An open circuit can also be caused by a failed connection in one of the electrical connectors that is used in a circuit.

The following procedure is a way to check for an open or a poor connection in a circuit.

Test For An Open Circuit

Table 1

Troubleshooting Test Steps	Values	Results
1. Identify Open Circuit A. Identify the connectors and the wire numbers of the suspect circuits. Use the Electrical System Schematic of the machine to identify the circuits. B. Turn the key start switch and the disconnect switch OFF. C. Disconnect the component and the ECM from the wiring harness. D. At one of the disconnected harness connections, place a jumper wire from the contact of the suspect wire to frame ground. E. At the other connector of the machine harness, use the multimeter probes to measure the resistance. Measure the resistance from the contact of the suspect wire to frame ground.	The resistance is less than 5 Ω.	OK - The harness circuit is correct. STOP NOT OK - The resistance is greater than 5kΩ. There is an open in the machine harness. Repair: Repair or replace the machine harness. Note: A resistance that is greater than 5 Ω but less than 5kΩ would indicate a loose connection or a corroded connection in the circuit. A resistance measurement that is greater than 5 kΩ would indicate an open in the circuit. STOP