Cat® Grade Control Cross Slope for Motor Graders Caterpillar

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 circuit for a lamp 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:

ReferenceFor a complete electrical schematic, refer to Electrical System Schematic for the machine that is being serviced.

TEST FOR A SHORT CIRCUIT.

1. Identify the connectors and the wire numbers of the suspect circuits. Use the Electrical System Schematic of the machine to identify the circuits.

2. Turn the key start switch and the disconnect switch to the OFF position.

3. Disconnect the components from the wiring harness.

4. At one of the disconnected harness connections, place one of the multimeter probes on the contact of the suspect wire.

5. Use the other multimeter probe to check the resistance across all other contacts in the connector(s) and frame ground.

   Expected Result: The resistance is greater than 5 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 the machine harness or replace the machine harness.

   Stop.