Case IH 517678-00 - BCM – BCM: Excessive electrical current draw or short circuit on the trailer brake lamp circuit

The system has detected an excessive electrical current draw (overload) or a short circuit on the trailer brake lamp circuit. The BCM deactivates the output to protect the wiring. This is typically caused by a dead short to ground in the trailer wiring harness, severe corrosion or moisture inside the 7-way trailer connector, or the trailer having too many traditional incandescent brake light bulbs.

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

1. 1

   Isolate the tractor from the trailer by disconnecting the plug, cycling the ignition key, and pressing the brake pedal to determine if the short is on the tractor or trailer side.

2. 2

   Inspect the 7-way trailer receptacle on the tractor and the plug on the trailer for green copper corrosion, packed dirt, water intrusion, or bent pins.

3. 3

   With the trailer disconnected, use a digital multimeter to measure the resistance (Ohms) between the brake lamp pin and the ground pin on the trailer's plug (a reading close to zero indicates a dead short).

4. 4

   Count the number of brake lamps on the trailer to evaluate if the combined amperage draw of multiple incandescent bulbs is too high for the BCM.

1. 1

   Clean or Replace the Connectors

   If corrosion or debris is found in the 7-way connectors, clean them thoroughly with electrical contact cleaner and a stiff brush. If the pins are loose, heavily pitted, or melted, cut off the old connector and wire in a new one.

2. 2

   Trace and Repair Trailer Wiring

   If a short to ground was detected, trace the brake light wire (often red or blue) from the plug to the rear lamps. Look for areas where the wire passes through metal frame holes or over axles where the insulation may have rubbed away. Cut out the damaged wire and repair it using heat-shrink butt connectors to keep moisture out.

3. 3

   Upgrade to LED Lamps

   If the wiring is perfectly intact but the trailer simply has 'too many loads' (too many incandescent bulbs), replace the incandescent brake lamp assemblies or bulbs with LED equivalents. LEDs draw a fraction of the amperage and will easily bring the total circuit load back under the BCM's maximum threshold.

4. 4

   Inspect Tractor Harness

   If the fault was present without the trailer connected, inspect the wiring harness on the back of the tractor. Look for pinched wires between the BCM and the rear 7-way receptacle, particularly around the 3-point hitch or rear axle housing.

5. 5

   Clear the Fault

   Once repairs are made, plug the trailer back in, turn on the tractor, and apply the brakes. The BCM should detect the correct load and restore power to the circuit. Clear the inactive fault code from the tractor's AFS Pro display.