Case IH 518986-03 - BCM – BCM: Work lamp #6 - short circuit to B+

The control module has detected battery voltage (12V) on the work lamp #6 circuit at a time when it should not be present, or the circuit is inappropriately drawing high voltage directly from a power source. This typically indicates that the power supply wire for this specific light is chafed and touching another live wire, or there is an internal short within a relay, switch, or the control module itself.

• MAGNUM AFS Connect
• Steiger AFS Connect
• Quadtrac AFS Connect

1. 1

   Inspect the physical housing of Work Lamp #6 for impact damage, water ingress, or melted connectors that could bridge the power terminals.

2. 2

   Disconnect the wiring harness at Work Lamp #6. Turn the system power switch to the RUN position (without activating the work lights) and use a digital multimeter to check for voltage at the harness connector. If 12V is present, the short to B+ is in the wiring harness or the BCM.

3. 3

   Disconnect the battery, the harness from the BCM, and the lamp. Test for continuity between the work lamp #6 control wire and the main battery power (B+) lines. If continuity exists, the wiring harness is pinched or melted together.

4. 4

   If the harness tests perfectly fine with no shorts to power, check the Body Control Module (BCM) for an internal high-side switch short.

1. 1

   Power Down

   Turn off the tractor ignition and disconnect the negative battery cable to prevent electrical arcing during repair.

2. 2

   Access the Circuit

   Locate Work Lamp #6 (refer to the operator's manual for the specific zone/location of lamp #6, usually a cab roof or fender light).

3. 3

   Trace the Harness

   Follow the wiring harness from the lamp back toward the cab entry point and the BCM. Pay special attention to pinch points, areas where the harness routes around sharp cab frame edges, or near moving suspension components.

4. 4

   Repair the Wiring

   If a chafed wire is found touching a 12V source, cut out the damaged section. Splice in a new section of wire using weather-sealed, heat-shrink butt connectors. Wrap the repaired section in protective loom and secure it with zip ties away from the pinch point.

5. 5

   Component Replacement

   If the wiring is intact but the lamp housing is internally melted/shorted, replace the work lamp assembly. If the BCM is outputting a constant 12V due to an internal hardware failure, the BCM must be replaced and reprogrammed by a dealer.

6. 6

   Reassembly and Clearing

   Reconnect the battery. Turn on the tractor and use the AFS Pro 1200 display to command the work lights ON and OFF. Verify that the light operates correctly and that the 518986-03 fault code changes from 'Active' to 'Inactive' so it can be cleared.