Case IH 517678-05 - BCM – BCM: Trailer Brake Lamps Current Below Normal or Open Circuit

The system has detected an "open circuit" in the trailer brake lamps. This means there is a gap in the wiring, a disconnected plug, a blown fuse, or the current draw on the trailer brake lamp circuit has dropped below the minimum threshold required for normal operation. The controller is trying to send power to the trailer brake lights but is not detecting a completed electrical path.

• MAGNUM AFS Connect
• Maxxum
• Puma
• Magnum
• Steiger

1. 1

   Isolate the trailer by disconnecting the implement from the tractor to determine if the fault is on the implement side

2. 2

   Visually inspect the 7-pin trailer socket at the rear of the tractor for terminal corrosion, dirt, or deformed contact tangs

3. 3

   Check the fuse panel for any blown fuses related to the trailer lighting or BCM auxiliary outputs

4. 4

   Measure the resistance in the brake signal circuit at the rear connector to verify continuity

1. 1

   Clean the Connector

   If corrosion or terminal deformation is found in the tractor's trailer socket, use an electrical contact cleaner and a terminal tool to clean and reshape the pins. If the socket is heavily corroded, cut and splice in a new receptacle.

2. 2

   Trace the Harness

   If the socket is in good condition, trace the wiring harness from the rear trailer socket forward to the BCM. Look for areas where the harness may have chafed against the chassis, experienced heat damage, or where inline connectors may have vibrated loose.

3. 3

   Repair Wiring

   If a broken wire is found, repair the open circuit using automotive-grade solder and weather-sealed heat-shrink tubing.

4. 4

   Test BCM Output

   If the wiring has perfect continuity from the BCM to the rear socket, use a multimeter to test the BCM output pin for the trailer brake lamps while an assistant presses the brake pedal. If the BCM fails to output voltage, the module itself may have suffered an internal hardware failure (such as a burnt internal circuit board) and will require replacement or a dealer reflash.