Case IH 520586-06 - BCM – BCM: Trailer left turn indicator - short circuit to ground

The controller has detected that the electrical current on the left turn indicator output circuit is exceeding normal limits, meaning the power wire is touching the chassis/ground before reaching the bulb.

• MAGNUM AFS Connect
• Maxxum
• Maxxum 100
• Maxxum 110
• Magnum series

1. 1

   Secure the vehicle to prevent it from rolling away.

2. 2

   Always disconnect the batteries before working on the vehicle's electrical system or testing continuity to ground.

3. 3

   Inspect the trailer socket at the rear of the tractor. Look for corrosion, water ingress, or crushed pins that could bridge the left turn signal pin to the ground pin.

4. 4

   Trace the wiring harness from the trailer socket back to the BCM. Look for areas where the wire insulation may have rubbed through against the frame (the frame acts as an earth return, and conductive connections to it will cause this short).

5. 5

   Disconnect any implement/trailer from the tractor and clear the codes. If the code does not return, the short circuit is in the trailer's wiring, not the tractor's BCM or harness.

1. 1

   Park the machine on a level surface, engage the parking brake, and turn off the engine.

2. 2

   Disconnect the negative battery cable.

3. 3

   If the diagnostic checks isolated the fault to the tractor's trailer socket, remove the mounting screws/bolts securing the socket to the bracket.

4. 4

   Disconnect the trailer socket wire harness connector.

5. 5

   Install the new trailer socket or replacement wire harness.

   Ensure the wiring is routed parallel to existing electrical cables and secured away from moving parts (like PTO shafts or gears) to prevent future damage.

6. 6

   Reconnect the battery.

7. 7

   Connect a diagnostic tool to the machine and navigate to the "Diagnosis" screen to clear the fault memory in the ECU/BCM.

8. 8

   Test the left turn signal with a known-good trailer or a 7-pin trailer plug tester to verify the repair.