John Deere 2386.03 – RLC (Roof Lighting Controller / Cab Roof Module) or CAB (Cab Module): Beacon Light Voltage High / Beacon Light Short to Power

The Roof Lighting Control Unit (RLC) has detected excessively high voltage in the electrical circuit for the beacon (flashing) light. The Failure Mode Identifier (FMI) .03 specifically indicates that the voltage is above normal or shorted to a high power source. This points to a specific electrical malfunction, such as a short to another power wire, an incorrect bulb altering circuit resistance, or a system-wide overcharging issue, rather than a simple open circuit or short to ground.

• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 8R Series (8245R to 8400R)
• 8RT Series
• 8RW Series
• 9RT Series (9470RT, 9520RT, 9570RT)
• 250D
• 300D Series II
• 260E
• 310E
• 944K Hybrid 4WD Loader
• 524KII Loader
• STS Series (9470 STS, 9570 STS)

1. 1

   Inspect the beacon light circuit wiring and connectors for signs of a short circuit to power, damaged insulation, pinched wires, or loose connections.

2. 2

   Verify the power supply to the beacon light is stable and under 16 volts, and inspect the alternator output for overcharging issues.

3. 3

   Ensure that the configuration of address RLC 056 is correct in the control software.

4. 4

   Test the beacon light directly to ensure it is functioning correctly and drawing the proper current/voltage without internal shorting.

1. 1

   Disconnect Power

   Turn off the machine and disconnect the battery to prevent electrical shock or further module damage.

2. 2

   Repair Wiring

   If the diagnostic checks revealed a short to power in the harness, repair or replace the compromised wiring and connectors.

3. 3

   Replace the Beacon

   If the wiring is intact but the beacon light itself has an internal short causing the voltage fault, remove the mounting bolt/nut from the DIN stem mount or bracket and disconnect the harness.

4. 4

   Install New Beacon

   Mount the replacement beacon light, secure the hardware, and plug in the electrical connector.

5. 5

   Clear Codes

   Reconnect the battery, turn the key to the ON position, and use a John Deere diagnostic tool (Service ADVISOR) to clear the RLC 002386.03 code. Test the beacon switch to verify the repair.