Case IH 520445-03 - BCM – BCM: Roof mounted headlamp low beam left - short circuit to B+

The control module has detected a short to battery voltage (B+) on the electrical circuit that supplies power to the left-hand low beam headlamp mounted on the cab roof.

• MAGNUM AFS Connect
• Magnum 180
• Magnum 200
• Magnum 220
• Magnum 240
• Magnum 250
• Magnum 280
• Magnum 310
• Magnum 340
• Magnum 380
• Magnum 400

1. 1

   Inspect the cab roof wire harness and headliner harness for chafing, melting, or pinched wires that could cause the left low beam circuit to short to a constant 12V power source.

2. 2

   Disconnect the left roof-mounted headlamp. With the tractor key ON but the headlight switch OFF, test the supply pin on the harness connector for voltage. If 12V is present, the harness is shorted to power.

3. 3

   Inspect the BCM connectors and the inline connectors between the cab roof and the main cab harness for water ingress, corrosion, or bent pins that could bridge the lighting circuit to a power wire.

4. 4

   Swap the left and right roof headlamps temporarily. If the code changes to the right side (520446-03), the headlamp assembly itself has an internal short. If the code remains 520445-03, the issue is strictly in the wiring or the BCM.

1. 1

   Park the tractor on a level surface, turn off the engine, remove the key, and disconnect the negative battery terminal to prevent electrical spikes.

2. 2

   Access the roof lighting harness.

   Depending on the exact short location, this may require removing the outer cab roof cap or dropping the interior headliner panel to access the routing.

3. 3

   Trace the wiring from the left roof headlamp back to the BCM, paying close attention to areas where the harness passes through the cab frame or near mounting brackets.

4. 4

   Once the short to B+ is located, repair the damaged wire using OEM-approved heat-shrink butt connectors, or replace the entire roof wire harness if the damage is extensive or melted.

5. 5

   Reinstall the headliner/roof cap and reconnect the headlamp.

6. 6

   Reconnect the battery, turn the key ON, and use the AFS Pro display or a diagnostic tool to clear the BCM fault codes.

7. 7

   Test the headlight switch to ensure the left roof low beam operates correctly without triggering the fault.