Case IH 520583-03 - BCM – BCM: Reverse lights - short circuit to B+

The control module has detected an electrical short to battery positive (B+) on the reverse light circuit, meaning the circuit is receiving voltage when it should not be (e.g., a power wire is touching the reverse light signal wire).

• MAGNUM AFS Connect
• Magnum 400 AFS Connect

1. 1

   Verify the condition by checking if the reverse lights remain illuminated continuously, even when the tractor is not in reverse gear.

2. 2

   Inspect the wiring harness running from the BCM to the rear reverse light assemblies. Look for melted wire insulation, chafing, or pinched wires where the reverse light circuit might be making contact with a constant 12V power source.

3. 3

   Disconnect the reverse light assemblies to determine if the short to battery positive is internal to the light housing or bulb socket.

4. 4

   Test the BCM output pins for the reverse lights to see if the module itself is internally shorted to power.

1. 1

   Disconnect the tractor's battery to ensure safety while working on the electrical system.

2. 2

   Access the reverse light assemblies at the rear of the tractor and disconnect their electrical connectors.

3. 3

   Trace the wiring harness from the reverse lights back to the Body Control Module (BCM).

4. 4

   Locate the section of the harness where the short to battery positive (B+) is occurring.

5. 5

   Repair the damaged wiring by splicing in new wire and sealing it, or replace the affected harness section entirely.

6. 6

   If the wiring is intact, inspect the reverse light bulb sockets for internal shorts. Replace the bulb or the entire light assembly if damaged.

7. 7

   If the harness and lights test good, the BCM may have an internal fault and may require replacement or a software update.

   OEM documents note a BCM 12V software update exists under part #91770803 for Magnum AFS Connect tractors.

8. 8

   Reconnect the battery, clear the fault codes, and test the reverse lights for proper operation.