All similar rocker switch LED backlight circuits are checked with this procedure. All backlight LED lamps are part of the rocker switches. The lamps are not replaceable.
The rocker switch backlight normal operation is:
Rocker switch is off - Backlight is off
Rocker switch is on - Backlight is on
If the backlight does not illuminate when the rocker switch is on, perform the following procedures:
Test Step 1. VERIFY THAT THE BACKLIGHT WILL NOT TURN ON
- Turn the keyswitch to the ON position.
- Turn the rocker switch to the ON position.
- Observe the backlight.
Note: Verify that the backlights are not dimmed. If the backlight is in bright sunlight, shield the backlight and make sure that the backlight is not on.
Expected Result:
The backlight is on.
Results:
- OK - The backlight is on. The problem does not exist at this time. Approve the machine for return to service. STOP.
- Not OK - The backlight is off. Proceed to Test Step 2.
Test Step 2. CHECK THE HARNESS FOR A POWER CIRCUIT OPEN OR A GROUND CIRCUIT OPEN
- Turn the keyswitch off.
- Disconnect all related ECMs from the harness.
- Disconnect the harness from the rocker switch.
- Obtain pin and wire numbers for the backlight circuit. Verify the pin and wire numbers in the Electrical Schematic of the machine you are working on.
- Measure the resistance in the harness between the contacts for the backlight and the corresponding contacts for the ECM.
Expected Result:
Each resistance is less than 5 ohms.
Results:
- OK - Each resistance is less than 5 ohms. The circuits in the harness are correct. The backlight LED lamp may have failed.
Repair: Replace the rocker switch containing the LED lamp.
Proceed to Test Step 3.
- Not OK - A resistance is greater than 5 ohms. A circuit is open in the harness.
Repair: Repair or replace the harness.
Proceed to Test Step 3.
Test Step 3. PERFORM AN OPERATIONAL CHECK
- Reconnect all connectors that have been removed.
- Turn the keyswitch on.
- Push the rocker switch to the ON position.
- Verify that the backlight is on.
- Push the rocker switch to the OFF position.
- Verify that the backlight is off.
Expected Result:
The backlight is on when the rocker switch is on and the backlight is off when the rocker switch is off.
Results:
- OK - The backlight is operating properly. Approve the machine for return to service. STOP.
- Not OK - The backlight is not operating properly. The ECM may have failed, however ECM failure is unlikely.
Repair: Contact your Cat® dealer. If the ECM must be replaced, refer to the Testing and Adjusting, "Electronic Control Module (ECM) - Replace" Section of this manual.
STOP.